QUICK ANSWER

Microsoft has confirmed known issues affecting some Windows 11 PCs after installing the August 27, 2026 KB5120998 Preview update.

The two problems Microsoft currently attributes directly to KB5120998 are:

1. Mouse customization settings may reset on non-English Windows installations.
2. Desktop backgrounds and some personalization settings may fail to load, resulting in a solid black desktop background.

Both problems affect Windows 11 version 24H2 and Windows 11 version 25H2.

Microsoft is working on fixes for both issues. At the time of writing, Microsoft has not provided a permanent workaround for either problem.

KB5120998 is a non-security Preview cumulative update, so users who have not installed it and do not specifically need its fixes or new features can generally wait for the next regular cumulative Windows update rather than installing the preview immediately.

COMPLETE ARTICLE

What Is Windows 11 Update KB5120998?

Microsoft released KB5120998 on August 27, 2026 as a cumulative Preview update for Windows 11.

It applies primarily to:

Windows version	Build after KB5120998
Windows 11 version 24H2	OS Build 26100.9278
Windows 11 version 25H2	OS Build 26200.9278

KB5120998 is a Preview/non-security update. Preview cumulative updates allow Microsoft to deliver quality improvements, fixes and selected new functionality before those changes become part of a later regular cumulative update.

The update contains many improvements, including changes involving Windows Search, File Explorer, networking/VPN reliability, cryptography, Windows Update, Task Manager, input and other Windows components.

However, Microsoft has subsequently documented problems affecting some systems.

Known Issue #1: Mouse Customization Settings Are Reset

One of the first problems Microsoft confirmed with KB5120998 concerns customized mouse pointers and cursor settings.

What happens?

After installing KB5120998 or a later Windows update containing the affected components, some users may find that Windows automatically reverts their mouse personalization settings to standard/default settings.

Affected settings can include:

• Custom mouse pointers
• Cursor appearance
• Cursor animations
• Settings configured through Mouse Properties

For example, if you normally use a customized pointer scheme, Windows may revert it to a standard cursor configuration.

Who is affected?

Microsoft says this issue specifically affects non-English Windows installations.

Affected client platforms include:

• Windows 11 version 24H2
• Windows 11 version 25H2

Windows Server is not listed as an affected platform for this issue.

Why does the problem occur?

According to Microsoft's investigation, the problem is associated with code components used by non-English Windows installations.

On affected systems, Windows fails to load the configured mouse personalization values correctly and therefore falls back to default settings.

Can you simply change the mouse settings back?

Unfortunately, this may not solve the problem.

The underlying problem is not necessarily that the saved mouse configuration has been deleted. Windows can fail to load the customized settings correctly.

Therefore, repeatedly changing the cursor settings may not provide a permanent solution.

Microsoft's status

Microsoft has confirmed the problem and is working on a resolution for a future Windows update.

At the time of writing, Microsoft has not published a permanent workaround.

Known Issue #2: Desktop Background Changes to Solid Black

Microsoft subsequently confirmed another personalization-related problem affecting KB5120998.

Some computers may lose their configured desktop background and display a solid black background instead.

Symptoms

After installing KB5120998 or later affected updates, users may notice:

• Desktop wallpaper disappears
• Desktop becomes completely black
• Slideshow background stops working
• Wallpaper configuration appears to reset
• Some contrast-theme settings may be affected
• Other Desktop personalization settings may fail to load

This can initially look like a graphics driver, Windows activation, Group Policy or corrupted user-profile problem.

However, on affected systems it may actually be a Windows update issue.

Why Does Windows Show a Black Background?

Microsoft explains that some Windows Desktop settings fail to load correctly.

When Windows cannot load the configured background, it can fall back to a default solid black background.

This is particularly important when troubleshooting the problem because repeatedly selecting another wallpaper may not fix it.

The wallpaper file itself may be perfectly valid.

The problem is that Windows is failing to correctly load the personalization setting.

Manually Changing the Wallpaper May Not Work

Normally you would fix a wallpaper problem by opening:

Settings → Personalization → Background

and selecting the wallpaper again.

With this particular KB5120998 problem, however, Microsoft states that manually restoring customized settings may not work because the issue prevents those settings from loading correctly regardless of the configured value.

Therefore, if the wallpaper immediately returns to black, do not automatically assume:

• the image file is corrupted,
• Windows is not activated,
• the graphics driver is defective,
• the user profile is damaged,
• Group Policy is blocking wallpaper changes.

First check whether KB5120998 or a later affected cumulative update is installed.

How to Check Whether KB5120998 Is Installed

Open:

Settings → Windows Update → Update history

Look under the update history for an entry containing:

KB5120998

You can also check from Command Prompt.

Open Command Prompt and run:

systeminfo | findstr /i "KB5120998"

If the update appears in the results, KB5120998 is installed.

You can also use PowerShell:

Get-HotFix -Id KB5120998

Note that Windows servicing architecture can sometimes make individual cumulative updates less straightforward to identify after they have been superseded. Checking Windows Update → Update history and the current OS build is therefore useful as well.

How to Check Your Windows 11 Build

Press:

Windows + R

Enter:

winver

and press Enter.

For the original KB5120998 release, the corresponding production builds are:

• Windows 11 24H2 – 26100.9278
• Windows 11 25H2 – 26200.9278

A later cumulative update will normally increase the build number.

Is the Microsoft Teams and New Outlook ARM Problem Caused by KB5120998?

This requires an important clarification.

Microsoft's KB5120998 documentation currently also displays a known issue where Microsoft Teams and the new Outlook for Windows might fail to launch or close unexpectedly on ARM-based devices.

Examples of affected hardware include ARM-based Copilot+ PCs such as:

• Surface Pro 11
• Surface Laptop 7

However, this problem did not originate with KB5120998.

Microsoft identifies its originating update as the August 11, 2026 security update KB5121003.

The issue is most likely to occur on newly configured or freshly imaged ARM PCs that have not yet received relevant Microsoft Store updates.

Classic Outlook, Word, Excel and other applications are not currently identified by Microsoft as affected by this particular problem.

Microsoft workaround for the ARM issue

Microsoft recommends:

1. Open Microsoft Store.
2. Go to Downloads.
3. Select Check for updates.
4. Install the latest Auto Super Resolution Package.
5. Ensure version 1.0.19.0 or later is installed.

This distinction matters: the ARM Teams/Outlook problem can appear on Microsoft's KB5120998 page because cumulative Windows updates carry forward applicable known issues, but it should not be described as a bug introduced by KB5120998.

Summary of Microsoft-Documented Problems

Problem	Originates with KB5120998?	Affected systems	Microsoft status
Mouse customization resets	Yes	Windows 11 24H2/25H2, non-English installations	Confirmed
Desktop background becomes black/settings reset	Yes	Windows 11 24H2/25H2	Confirmed
Teams/new Outlook may fail on ARM PCs	No – originates with KB5121003	Certain ARM-based Windows PCs	Workaround available
Windows Server affected by the two KB5120998 personalization bugs	No known impact documented	Windows Server	Not listed as affected

Should You Install KB5120998?

For most users, there is an important point to understand:

KB5120998 is a Preview update, not a normal monthly security update.

Preview updates are useful for:

• testing upcoming Windows fixes,
• obtaining a specific non-security fix early,
• IT administrators validating upcoming changes,
• users who specifically need one of the improvements included in the update.

If your computer is stable and you do not need a specific fix delivered by KB5120998, there is generally less reason to rush to install an optional Preview update.

The improvements from preview releases are normally incorporated into subsequent cumulative Windows servicing.

Business and managed computers

For business PCs, IT administrators should test preview cumulative updates on a limited number of machines before wider deployment.

This is particularly advisable when organizations use:

• customized Windows environments,
• non-English Windows installations,
• custom cursor configurations,
• centrally managed personalization,
• ARM-based Windows devices,
• specialized business applications.

What Should You Do If KB5120998 Is Already Installed and Everything Works?

Nothing special is required.

The existence of a Microsoft-confirmed known issue does not mean every computer running KB5120998 will experience it.

If:

• your wallpaper is working,
• mouse settings remain intact,
• applications work normally,
• Windows is stable,

there is no reason to make unnecessary system changes solely because the update has documented known issues.

Continue installing normal Windows servicing updates as appropriate.

What Should You Do If Your Wallpaper Has Turned Black?

First confirm whether the problem began after installing KB5120998 or a later update containing the affected components.

Check:

Settings → Windows Update → Update history

If the timing matches Microsoft's documented issue, avoid immediately performing aggressive troubleshooting such as:

• deleting the Windows user profile,
• resetting Windows,
• reinstalling graphics drivers repeatedly,
• deleting personalization registry keys,
• reinstalling Windows.

The problem may be caused by the Windows update itself.

Because Microsoft says manually restoring the affected personalization setting may not work, waiting for Microsoft's servicing fix may be preferable unless the issue is seriously affecting your workflow.

What Should You Do If Your Mouse Cursor Keeps Resetting?

If you are using a non-English Windows installation and your custom cursor or cursor animation began resetting after KB5120998, the symptoms match Microsoft's documented issue.

You can verify your configured settings through:

Control Panel → Mouse → Pointers

or run:

main.cpl

However, Microsoft warns that manually restoring the values might not resolve the problem because Windows may continue failing to load those values correctly.

For that reason, repeatedly modifying registry entries or recreating cursor configurations is unlikely to address the underlying Windows bug.

Can KB5120998 Be Uninstalled?

If KB5120998 causes serious problems, you can check whether Windows offers an uninstall option.

Navigate to:

Settings → Windows Update → Update history → Uninstall updates

Find KB5120998 if it is available for removal.

Administrators can also inspect installed packages using DISM:

DISM /Online /Get-Packages

Important warning

Do not remove Windows updates unnecessarily.

Cumulative update servicing can be affected by newer updates, and an update may no longer be independently removable after it has been superseded.

If a newer cumulative update has already replaced KB5120998, installing the latest available fixed update is normally preferable to attempting to remove older servicing packages manually.

Do Not Use DISM Package Removal Without Understanding the Consequences

Advanced administrators may find Windows packages using DISM, but manually removing servicing packages using commands such as:

DISM /Online /Remove-Package

should not be treated as the first troubleshooting method.

Removing the wrong servicing package can cause:

• Windows Update problems
• servicing corruption
• boot problems
• inability to install future cumulative updates

Use the supported Uninstall updates interface whenever possible.

Can You Skip KB5120998?

If Windows is only offering KB5120998 as an optional Preview update and you have not installed it, you can choose not to install it.

This does not mean you should stop installing Windows security updates.

There is an important difference between:

Optional Preview cumulative update

and

Monthly security cumulative update

Security updates should generally be installed according to your normal Windows update or organizational patch-management policy.

KB5120998 Is Also a Major Feature and Servicing Update

Despite these known issues, KB5120998 contains a large collection of improvements.

Among Microsoft's documented changes are improvements involving:

• multiple virtual desktops,
• Display settings reliability,
• Task Manager app history,
• Windows Setup,
• Windows Update restart behavior,
• application update coordination,
• networking,
• VPN reliability,
• Japanese IME reliability,
• voice typing,
• accessibility,
• touchpad reliability,
• Outlook search on Japanese Windows systems,
• cryptography.

The update also introduces additional support for post-quantum cryptography, including standalone ML-KEM use for TLS key exchange.

Another significant change is Microsoft's continuing removal of the legacy WMIC command-line utility from Windows 11 24H2 and 25H2.

Therefore, KB5120998 is more than a small bug-fix release, which makes testing especially important in managed environments.

KB5120998 and WMIC Removal

Starting with Microsoft's August 2026 Windows servicing changes, WMIC is no longer included with Windows 11 versions 24H2 and 25H2.

This does not mean Windows Management Instrumentation itself has been removed.

WMI remains supported.

What is being removed is the legacy:

wmic

command-line utility.

Administrators and scripts that still depend on WMIC should migrate to supported alternatives such as PowerShell CIM cmdlets.

For example, instead of:

wmic computersystem get model

PowerShell can use:

Get-CimInstance Win32_ComputerSystem | Select-Object Model

Organizations should therefore test older scripts and support utilities that still call wmic.exe.

KB5120998 Troubleshooting Checklist

If problems started after installing KB5120998, use the following checklist before making major Windows changes.

Step 1 – Check the Windows build

Run:

winver

Step 2 – Check Windows Update history

Navigate to:

Settings → Windows Update → Update history

Step 3 – Identify the symptom

Determine whether you are experiencing:

• black desktop wallpaper,
• wallpaper resetting,
• slideshow settings disappearing,
• contrast-theme changes,
• custom cursor resetting,
• cursor animation resetting,
• another unrelated Windows problem.

Step 4 – Compare the symptom with Microsoft's known issues

Do not automatically attribute every problem occurring after an update to that update.

Only two personalization problems are currently documented by Microsoft as originating with KB5120998.

Step 5 – Install newer Windows updates when available

Check:

Settings → Windows Update → Check for updates

Microsoft has stated that it is working on resolutions for the confirmed issues.

Step 6 – Avoid destructive troubleshooting

Do not immediately:

• reset Windows,
• delete user profiles,
• modify servicing registry keys,
• remove random Windows packages,
• use third-party update removal utilities.

A Microsoft-confirmed servicing problem should ideally be corrected by Microsoft's subsequent servicing update.

Important Note for IT Administrators

KB5120998 demonstrates why optional Preview updates should normally be deployed through a controlled testing process in business environments.

A practical deployment model is:

Test PCs → Small pilot group → Wider deployment

Before broad deployment, verify:

• business applications,
• printing,
• VPN connectivity,
• Remote Desktop,
• Microsoft 365 applications,
• endpoint-security software,
• custom scripts,
• PowerShell automation,
• login scripts,
• desktop personalization policies,
• Group Policy,
• device-management policies.

This becomes especially important when Windows updates introduce platform-level changes rather than simply security patches.

FAQ

Is KB5120998 causing black wallpaper in Windows 11?

Yes. Microsoft has confirmed that some Windows 11 systems can fail to load Desktop personalization settings after updates beginning with KB5120998, resulting in the desktop displaying a solid black background.

Does KB5120998 reset mouse settings?

Yes, on affected non-English Windows installations. Microsoft says customized cursor and cursor-animation settings can revert to standard settings.

Which Windows versions are affected by the KB5120998 problems?

Microsoft lists Windows 11 version 24H2 and Windows 11 version 25H2 as affected by the mouse-personalization and desktop-background issues.

Is Windows Server affected?

Microsoft does not list Windows Server as an affected platform for these two KB5120998 personalization issues.

Can I fix the black background simply by selecting my wallpaper again?

Not necessarily. Microsoft says manually restoring customized settings might not work because the problem prevents Windows from loading those settings correctly.

Can I fix the mouse problem by selecting my cursor again?

It may not remain fixed. Microsoft says the affected Windows components can fail to load the customization regardless of the configured value.

Has Microsoft fixed the KB5120998 problems?

As of September 7, 2026, Microsoft says it is working on resolutions for the mouse-customization and desktop-background problems in future Windows updates.

Does KB5120998 cause Microsoft Teams and Outlook to crash?

Microsoft's KB5120998 page lists an ARM-related Teams/new Outlook issue, but Microsoft identifies its originating update as KB5121003 from August 11, 2026, not KB5120998.

Is there a workaround for the Teams and Outlook ARM issue?

Yes. Microsoft recommends updating the Auto Super Resolution Package to version 1.0.19.0 or later through Microsoft Store.

Is KB5120998 a security update?

No. KB5120998 is an August 2026 cumulative Preview/non-security update.

Should I uninstall KB5120998?

Not automatically. If your system works correctly, there is generally no need to uninstall an update merely because Microsoft has documented issues affecting some systems. If your computer is affected, check for newer Windows updates and Microsoft's latest guidance before uninstalling it.

Can I skip KB5120998?

If it is still being offered as an optional Preview update and you do not need its fixes, you can generally wait for normal Windows servicing. This should not be confused with skipping regular security updates.

Does KB5120998 remove WMI?

No. Windows Management Instrumentation remains supported. Microsoft is removing the legacy WMIC command-line utility, not WMI itself.

How can I check whether KB5120998 is installed?

Open:

Settings → Windows Update → Update history

You can also try:

Get-HotFix -Id KB5120998

and check your Windows build using:

winver

FINAL RECOMMENDATION / CONCLUSION

Windows 11 KB5120998 delivers a substantial collection of improvements, but Microsoft has now confirmed two significant personalization problems originating with the update.

The most important known issues are:

1. Mouse cursor and animation customization can reset on non-English Windows installations.

2. Desktop personalization settings can fail to load, causing wallpaper to be replaced by a solid black background.

Microsoft is working on fixes for both issues.

Users who already have KB5120998 installed and are experiencing no problems do not need to make unnecessary changes.

Users experiencing the documented symptoms should avoid aggressive troubleshooting such as deleting profiles, modifying servicing components or reinstalling Windows, because the underlying cause may be the Microsoft-confirmed update issue.

For business environments, KB5120998 is another reminder that optional Preview Windows updates should be tested before organization-wide deployment.

Because Microsoft's known-issues documentation can change as investigations progress, administrators should check Microsoft's latest Windows Release Health and KB5120998 documentation before making deployment or rollback decisions.

 

#KB5120998 #Windows11 #Windows11Update #WindowsUpdate #Windows11Problems #Windows11Bugs #KnownIssues #Microsoft #MicrosoftWindows #Windows1124H2 #Windows1125H2 #Windows24H2 #Windows25H2 #BlackWallpaper #BlackBackground #DesktopBackground #WindowsWallpaper #MouseSettings #MouseCursor #CursorReset #MouseProblem #WindowsPersonalization #WindowsTroubleshooting #WindowsSupport #WindowsFix #WindowsUpdateError #WindowsUpdateProblems #WindowsUpdateTroubleshooting #CumulativeUpdate #PreviewUpdate #OptionalUpdate #WindowsBuild #261009278 #262009278 #MicrosoftSupport #WindowsReleaseHealth #ITSupport #ITAdministrator #SystemAdministrator #SysAdmin #WindowsAdmin #WindowsTips #WindowsSecurity #ARMWindows #MicrosoftTeams #MicrosoftOutlook #WMIC #WMIRemoval #PowerShell #BisonKnowledgebase