External display no longer recognized on MacOS 12.3

Hello cowomo404,

It sounds like you're having trouble with you external display being recognized. First, check for any firmware updates for your displays.

Next, start up in safe mode to see if the display is detected while in safe mode: How to use safe mode on your Mac

Take care.

I did have a similar issue. External 4k Monitor connected via USB-C was not recognised after update to 12.3.

The following did help in my case.

• Unplugged Monitor from Mac
• Unplugged Monitor from Power
• Restart of Mac
• Re-plug Monitor using USB-C cable to Mac
• Power-on Monitor

Since then Monitor is recognised again by the MBP M1Pro.

This is how I resolved.

Here is the latest with a work-around. Reinstalling the OS did not resolve, so went old school and used an HDMI Cable to Mac Mini versus a DP or USB C and the OS booted like normal. Also display scaling is working as expected using HDMI.

Hope this helps. Likely a fix coming soon from apple, so that we can all use our USBC or DisplayPort interfaces again.

This is how I resolved.

Here is the latest with a work-around. Reinstalling the OS did not resolve, so went old school and used an HDMI Cable to Mac Mini versus a DP or USB C and the OS booted like normal. Also display scaling is working as expected using HDMI.

Hope this helps. Likely a fix coming soon from apple, so that we can all use our USBC or DisplayPort interfaces again.

Good to hear. The issue that others have run into where unplugging/reboot does not resolve appear to be Intel Based Macs, where users have gone to the extreme of reinstalling the OS from recovery.

Support has the use case I provided submitted to their engineering/2nd level support teams to try and replicate.

I really wish I would have seen this before I updated. I have a brand new Mac Mini with two external monitors via Thunderport. Everything worked until I updated last night, now only one monitor at a time works, regardless of the port I'm using. I've tried HDMI, Thunderport and DisplayPort. So far, none of the fixes have worked.

I also had a perfectly functioning MacMini, 3.2 GHz 6-Core Intel Core I7, 64 GB 2667 MHz DDR4, with an external ViewSonic VA2759-smh monitor. This monitor is now discontinued, purchased in 2019, and no new firmware is available for it by ViewSonic, but the monitor had been fully recognized by my Mac mini upon restart from sleep, under macOS Monterey 12.2.x, so it seems as if 12.3 was not actually ready for RC (release candidate) status when it was pushed out to the masses, not if perfectly functional monitors on still supported Mac mini platforms are rendered faulty! Please pardon my frustrated tone about this matter.

I am curious when we can expect 12.3.1? to remedy this obvious external monitor issue; or will I be forced to find a new monitor

I use a SMK Link dongle for power (and ethernet). After today's update it wouldn't even detect the dongle (so no power) so then the external monitor (which plugs directly into the Air) wasn't detected either. I unplugged and plugged the dongle in a dozen times, reset PRAM (held power button for seven seconds, but I don't think it doesn't anything on an M1). Eventually the dongle was detected and got power to the Mac and then the monitor was detected. But not idea if this will happen again.

So my first attempt after the update made things worse

I have the same issue with my LG 4k Monitor connected via USB-C to my MBP M1Pro.

Sad Mac :-(

Have an open Case with Apple, related to the similar issues on the mac mini, switched to HDMI to resolve until a fix can be released.

I have the same issue. M1 MacBook Air

Until there is an Apple fix I would not use sleep. Just use screen saver.

12.3.1 is out. May fix the issue.

repeat