Downloaded Monterey upgrade.
Have my latest Big Sur installed on my MacBook Pro Retina Mid 2015.
The upgrade preparation runs for +/- 1 hour, after which MacBook reboots.
After reboot, instead of upgrading, my MacBook return to Big Sur login screen.
Tried 5 times, after which I tried also secure restart, but nothing helps.
Monterey simple won't upgrade ...
Check the About this Mac window. If you're still on Big Sur try the following;
#1 - boot into Safe Mode according to Start up your Mac in safe mode - Apple Support.
NOTE: Safe Mode boot can take up to 3-5 minutes as it's doing the following;
• Verifies your startup disk and attempts to repair directory issues, if needed
• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)
• Prevents Startup Items and Login Items from opening automatically
• Disables user-installed fonts
• Deletes font caches, kernel cache, and other system cache files
#2 - go to the System/Software Update preference pane and begin the download.
#3 - run the installer from the Safe Mode.
I've had better luck from the Safe Mode because I evidently have some 3rd party software that interferes with the installation.
Have you logged in and clicked on About This Mac? After my upgrade from Big Sur to Monterey the login screen is identical to the old one, desktop picture and all.
Monterey Upgrade
