Re: Re. Update
Are you absolutely sure?
Look at what happened with 20H2, that somehow got onto secure systems despite in many cases admins actually stopping all updates. It got through and caused complete mayhem.
Best guess is that other machines were hosting the update(s) as is enabled by design which bypassed the usual blocks so someone bringing in a laptop with it installed was all it took.
It wouldn't be much of a stretch to block specific file content, and as I mentioned very hard to undo.
Just to give folks here an idea of the lengths certain authorities go to, it was possible for a piece of malware to get into the uEFI BIOS on a system here, and completely block access to an entire drive even on a clean booted system having worked perfectly the day before.
Even cloning the drive didn't help as none of the usual programs would work: the error message suggested a sector alignment issue but cloning everything manually to an identical drive also didn't work.
The only thing which made any difference was using a standalone box which copied everything except that specific multi-part .ZIP archive suggesting it was the underlying cause of the problem.