Here are the steps I have taken:
Reset WU by stopping services, renaming SoftwareDistribution and Catroot2.
Run the WU troubleshooter, which said there was "database corruption" that it was unable to fix.
Run DISM "restorehealth," which failed on "Error 14," "not enough storage"
Run sfc successfully.
The most recent is cumulative update is KB5004238, which reaches 100% but reports failed after reboot. Behavior is the same through Windows Update and manual install. Error is 0x80073716, ReportingEvent.Client.181, Unable to find resource.
This is making me crazy. I had a similar issue on my Win10 machine, and finally did a fresh installation. I don't really want to do this on my server.
I've attached my CBS log folder.