Fix Windows Update Standalone Installer Failed with error 0x800f0838 in Windows 11/10 by following these working solutions.

If you get Windows Update Error 0x800f0991 on Windows 11 on Insider or Stable builds, first check if these two Update-related Services are running.

Although the most common cause of this issue is the Windows Installer service, other factors include corrupted Windows update files and problems with the registry values.