Big Sur creates a strange shutdown; incompatible with something, but what???
Ever since Big Sur installed itself, when I shut down my (2 month old) iMac the screen flashes totally black and then the usual background reappears divided in two: the left half has a dull filter over it while the right half is bright 5K. There is a clear line down the middle of the two halves.
I tried deleting apps and sometimes got a normal shutdown, sometimes not.
Tried ejecting every single attached drive or USB device and sometimes got a normal shutdown, sometimes not.
WIPED THE ENTIRE HARD DRIVE BACK TO FACTORY SETTINGS and reinstalled from Time Machine only user settings and apps, and the problem came right back, so it's somewhere in the user settings or apps. (I have been deleting non-essential apps left and right.)
Apple Support has not been helpful. They ended up sending me to the Apple Store where the computer was examined and restored to factory settings. It is not a hardware issue, so they don't seem to know what to do.
I don't want to go back to factory settings again. I have already lost almost a week of work over this.
I need a basic way to inventory what there is about my user settings or apps that could be conflicting with Big Sur.
Is it hard to run a diagnostic that does that?
iMac Line (2012 and Later)