Just restarted your computer and found that the mouse pointer has become large and white, and the desktop wallpaper has mysteriously turned solid black—if you've recently run into this situation, chances are you installed Windows 11's KB5120998 update. This update is an optional preview update that Microsoft pushed out on August 27, 2026. While it brought some new features, it also introduced several frustrating bugs. Microsoft has confirmed the related issues in the Windows release health dashboard and says it is investigating.

This article will help you understand: what KB5120998 actually is, what problems it may cause, how to determine whether you are affected, and most importantly—how to safely uninstall it and restore your system to normal.

What Is KB5120998? Which Systems Will Receive It

KB5120998 is the August 2026 optional preview update for Windows 11 (a non-security update), applicable to both Windows 11 24H2 and 25H2. After installation, systems on 25H2 rise to Build 26200.9278, while 24H2 rises to Build 26100.9278.

It belongs to the "D release" preview updates, which are essentially pretests for the following month's official patch. These updates do not install automatically unless you manually select them in "Settings > Windows Update > Advanced options > Optional updates," or you have enabled the "Get the latest updates as soon as they're available" toggle.

The main changes brought by this update include: the taskbar position can be freely adjusted (bottom, top, left, right), the Start menu has added size options, and the Windows search interface is cleaner with reduced interference from Bing search results.

Typical Problems That May Appear After Installation

According to extensive user feedback and Microsoft's official confirmation, KB5120998 mainly causes the following categories of problems:

Mouse cursor abnormalities are the most common symptom. Users report that custom cursor colors and sizes are reset to standard settings, some high-DPI cursors are replaced with larger white cursors, and manually restoring the settings may fail again.

Desktop background turning black is also very common. After installing the update, desktop wallpaper and solid color background settings reset to black after every restart, and manually setting them again does not persist.

In addition, some users report taskbar pinned icons displaying as gray squares, lost personalization settings, and other issues. Notably, some users found that newly created user profiles on the same computer are unaffected, indicating that the problem lies in the state of the original user profile.

How to Confirm Whether You Have KB5120998 Installed

Before taking any action, first confirm whether your system actually has this problematic update installed. There are two methods:

Method 1: Check through update history

  1. Open "Settings" (Win + I)
  2. Click "Windows Update" on the left
  3. Click "Update history"
  4. Look for "2026-08 Preview Update (KB5120998)" in the list

Method 2: Confirm the version number through the command line

Press Win + R, type winver, and press Enter. If the OS internal build shown is 26200.9278 or 26100.9278, KB5120998 has been installed.

Complete Steps to Uninstall KB5120998

If you confirm that the problem is caused by this update, uninstalling it is currently the most effective solution. Below is the standard uninstall process:

  1. Open "Settings" (Win + I), and go to "Windows Update"
  2. Click "Update history"
  3. Scroll to the very bottom of the page and click "Uninstall updates"
  4. In the list that pops up, find "2026-08 Preview Update (KB5120998)"
  5. Click the "Uninstall" button on the right
  6. Confirm the operation as prompted, and wait for the uninstall to complete
  7. Restart your computer

After restarting, check whether the mouse cursor and desktop background have returned to normal.

Note: Some users report that KB5120998 may not appear in the "Uninstall updates" list, or that after uninstalling, the system says "This update is required and cannot be uninstalled." If you encounter this situation, you can try the following alternatives:

  • Go to "Settings > System > Recovery," and click "Restart now" next to "Advanced startup"
  • After restarting, select "Troubleshoot > Advanced options > Uninstall updates > Uninstall the latest quality update"
  • If it still does not work, you can enter the Windows Recovery Environment (WinRE) and use the command line to run DISM /Online /Remove-Package /PackageName:Package_for_RollupFix~31bf3856ad364e35~amd64~~26100.9278.1.35 (administrator privileges required)

Prevent KB5120998 from Being Reinstalled

After uninstalling, Windows Update may push this optional update again the next time it checks. To prevent it from being automatically reinstalled, it is recommended to turn off the following toggle:

  1. Open "Settings > Windows Update"
  2. Click "Advanced options"
  3. Turn off the "Get the latest updates as soon as they're available" toggle

This setting can prevent optional preview updates from being automatically installed on your device.

In addition, you can also clear the Windows Update cache to further prevent reinstallation: open File Explorer, navigate to C:\Windows\SoftwareDistribution\Download, delete all contents in that folder, and then restart your computer (note: restart, not shut down and then power on).

Summary and Daily Prevention Tips

Key points to review: KB5120998 is an optional preview update for Windows 11 that causes mouse cursor resets and desktop background turning black. Uninstalling the update is currently the most reliable fix, and after uninstalling, remember to turn off the "Get the latest updates" option to prevent reinstallation.

Daily prevention tips:

  • For patches labeled "preview update" or "optional update," if you do not urgently need the new features they contain, it is recommended to wait one to two weeks and observe community feedback before deciding whether to install them
  • Before installing any system update, develop the habit of backing up important data and creating a system restore point. Path to create a restore point: search "Create a restore point" → select the system drive → click "Create"
  • Microsoft has fixed the cursor style failure and desktop wallpaper black screen issues in the September 2026 cumulative update. If you want to completely resolve the issue, you can wait for and install the September official cumulative update (KB5124008) after uninstalling KB5120998