mac mini m1 2020 stopped recognizing my second monitor

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Level 1

4 points

mac mini m1 2020 stopped recognizing my second monitor

I have a Mac Mini m1 2020 with dual external monitors. One (a Samsung monitor) is hooked up to the HDMI port and the other one (an Acer monitor) is hooked up to the USB -C port. They were both working well together for quite a while and suddenly the second monitor stopped being recognized. They both still work perfectly if I disconnect the other one (so if I disconnect the samsung monitor the computer recognizes the acer monitor, and if I disconnect the acer monitor the computer recognizes the samsung monitor). It's only when they are BOTH connected that the computer then only recognizes one of them (generally the one that is connected via USB-C). I've tried the "Detect Display" option in system settings and I've tried new cables. The mac mini is up-to-date with system updates, though I can't tell when the last update was done (I have the mac mini set to autoupdate).

Does anyone know what might have happened?

Posted on Sep 3, 2025 11:23 AM

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Answer 1

Sep 4, 2025 03:36 PM in response to dhg63

This might have been caused by a bug in a Sequoia update. There have been reports on these forums of dual-monitor setups stopping working after people updated to a certain version of Sequoia 15.5.

I believe that the fix was to delete a certain user-level preference file and restart the Mac.

To remove the file using the Finder:

Hold down the Option key and select Library from the Go menu.
Go into the Preferences folder, then into the ByHost folder inside of it.
Delete the .plist (property list) file whose name begins with com.apple.windowserver.displays (there will be a very long hexadecimal string between this prefix and the .plist extension)

To remove the file using the command line (Terminal):

rm ~/Library/Preferences/ByHost/com.apple.windowserver.displays.*.plist

After removing the file, restart the Mac. The idea is it should automatically regenerate a new copy.

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Answer 2

dhg63 Author

Level 1

4 points

Sep 6, 2025 10:48 AM in response to Servant of Cats

Thanks for the suggestion. I tried this option but it has not resolved the issue.

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