PSP ALERT - buggy .dll causes screen blink. So it fails then Windows reinstalls etc. looping blink which shows up after logging in and in safe mode.
C:\Program Files\Corel\Corel PaintShop Pro 2021 (64-bit)\psppthumbshellext64.dll
My PC Repair replaced with http://www.cherubicsoft.com/en/projects/sagethumbs
I have access to my system back.
UPDATE - A letter is being sent to Corel to alert them of the issue.