Win8.1 updates failing for months

I just noticed that nearly all of my Windows updates have been failing since 4/17/2022:

Just a few exceptions succeeded:

I tried following the suggestions at:
https://www.800error.com/KB2962409-windows-update-error-knowledge-kb-ms-security-fail

1. Stopping the Windows Update service and clearing
   C:WindowsSoftwareDistributionDataStore

   (then restarting the service, of course) didn’t help
2. When I tried running
   C:Windowssystem32>sfc/scannow

   I got this message:
   Beginning system scan. This process will take some time.
Windows Resource Protection could not perform the requested operation.

3. I looked at the Registry but found that
   HKEY_LOCAL_MACHINESOFTWAREPoliciesMicrosoftWindowsWindowsUpdate

   had neither WUServer nor WIStatusServer

When I tried to run Windows Update again, it just keeps checking endlessly.

Upgrading to Windows 10 (or 11) isn’t at all an option now, so I would truly appreciate help getting the updates for 8.1 working.

What else could I do to get all those updates applied?