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Going Fullscreen Freezes my iMac

I have a iMac 21.5inch from late 2015. When ever I play a video on full screen or my screen saver goes off, it completely freezes my Mac to the point I have to reboot it. The screen also slightly flickers sometimes. I have 750 gb left. This started happening when I upgraded to Big Sur. What could be the issue? Thank you.

iMac Line (2012 and Later)

Posted on Feb 17, 2021 3:12 PM

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Question marked as Top-ranking reply

Posted on Feb 17, 2021 3:15 PM

Boot into Safe Mode by booting with the Shift key held down and check there to see if the problem persists.  Reboot normally and test again.


NOTE: Safe Mode boot can take up to 10 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


1 reply
Question marked as Top-ranking reply

Feb 17, 2021 3:15 PM in response to Mrokmaracd

Boot into Safe Mode by booting with the Shift key held down and check there to see if the problem persists.  Reboot normally and test again.


NOTE: Safe Mode boot can take up to 10 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


Going Fullscreen Freezes my iMac

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