KB5077181 was released about a month ago as part of the February Patch Tuesday rollout. When the update first arrived, users reported a wide range of problems, including boot loops, login errors, and installation issues.
Microsoft has now acknowledged another problem linked to the same update. Some affected users see the message “C:\ is not accessible – Access denied” when trying to open the system drive.
I have no scientific sources I can point to to back it up. A hunch is what it is, ultimately. It seems true to me, but I suppose I could be wrong. I suspect it’s difficult to really prove this one way or the other.