How to fix windows 11 update error 0x800f0991?

The Windows 11 update error 0x800f0991 typically indicates a problem related to Windows Update, often involving issues with the update components, system files, or network connectivity. It can also be related to problems with the Windows Update service not being able to download or install the necessary files properly.

Common causes of Windows 11 update error 0x800f0991:

• Corrupted Windows Update components
• Problems with the Windows Update cache
• Insufficient disk space
• Network connectivity issues
• Problems with the Windows Update server
• Corrupted system files
• Issues with specific update files or dependencies

How to troubleshoot and fix Windows 11 update error 0x800f0991:

1. Run Windows Update Troubleshooter:
    Go to Settings > System > Troubleshoot > Other troubleshooters.
    Select Windows Update and click Run.
    Follow the prompts to detect and fix issues.
2. Clear the Windows Update cache:
    Open Command Prompt as Administrator.
    Run these commands one by one: net stop wuauserv net stop bits
    Navigate to C:\Windows\SoftwareDistribution\Download and delete all files inside.
    Restart the services:
3. Run System File Checker and Deployment Image Servicing and Management (DISM): 
    Open Command Prompt as Administrator.
    Run: sfc /scannow
    Then: DISM /Online /Cleanup-Image /RestoreHealth
    After completion, restart your PC and try updating.
4. Check for sufficient disk space:
    Ensure you have enough free space on your system drive (usually C:).
5. Manually download and install the update:
    Visit the Microsoft Update Catalog.
    Search for the specific update KB number.
    Download and install it manually.
6. Reset Windows Update components:
    Use a script or manually reset the update components.
7. Check your network connection:
    Ensure a stable internet connection.
    Disable VPNs or firewalls temporarily to rule out interference.