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Catalina update (Nov. 5, 2020) broke display mirroring

V

varxx

macrumors member
Original poster
Dec 12, 2012
37
7
I usually run my 2017 MacBook Pro connected to an external monitor. Since installing the supplemental update to Catalina (10.15.7, released Nov. 5, 2020), display mirroring no longer functions properly. It hops back and forth incessantly, alternately blanking the external monitor but leaving the MacBook's built-in monitor working.

This setup had been working without a hiccup for over a year. Now it's gone caflooey.

If I turn off "Mirror Displays" and extend the display from my MacBook to the external monitor, the display is stable. This isn't the setup I want to use, however.

Any ideas?

My system:

macOS Catalina 10.15.7
MacBook Pro (13-inch, 2017, four thunderbird 3 ports), 3.5 GHz Duel-Core Intel Core i6 with 16GB Ram.
Graphics: Intel Iris Plus Graphics 650 1536 MB
External monitor: Dell P2414H

Thanks.
 
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