12.3 update breaks external monitor on mac mini 2018

Since Safe mode works and therefore Safe Mode will only load the barebones native Apple Kernel extensions - it is reasonable to conclude there is some more involved in this issue.

Not sure of direction other to take other to ask is there any Third Party Software directly involved in operating this Benq Monitor

Outside of that - maybe a more Learned Collegue with better Hardware knowledge will pickup up your question and have more insights

I have a 2018 Mac Mini, connected to two external 27" LG displays. The set-up was working fine pre-12.3. After 12.3, at best I could get one monitor recognised, but even that was more by luck. Most of the time, I had the black screen after boot, as reported by OP. Also as reported, safe mode was ok to at least get a working display.

I also suspected that I might have 3rd party software that was unfortunately interferring with the MacOS update. So I reformatted my drive, deleting everything from the computer, and reinstalled MacOS. No difference. Still not working.

Switching connections between thunderbolt, usbc and HDMI yeilded no satisfactory results.

Then I found this article and switched my monitors from Displayport 1.4 to Displayport 1.2, as per the suggestion. This worked.

So, I would suggest from this that the problem is unlikely to be related to 3rd party, user installed software and more likely solely related to Apple's update.

The question is surely: why does an Apple update require the downgrade of Displayport version to fix things? This is wholly unacceptable.

My 2019 MacBook Pro just upgraded to 12.3 and I can not longer use my BenQ PD3220U. I have downgraded the monitor to DP 1.2, but this does not help for me.

My experience is when the monitor is connected, the MacBook display goes black and then dim and cycles thru these two states while something takes up background CPU usage, causing the fans to come on. The BenQ remains off with no signal detected and I can't do anything on the Macbook. Keyboard and mouse frozen. I have to unplug the Thunderport cable to be able to use the MacBook again.

Does your monitor have a DVI or VGA input, if so see if they work with a USB-C adapter. The reason I ask is that I use this for an extended display on my M1 iMac running MacOS 12.3.

I’m wondering if the elephant in the room causing this issue is Universal Control affecting the use of non-DVI/VGA methodology.

Unfortunately the BenQ PD3220U does not have a DVI or VGA, just Thunderbolt-3, HDMI, DisplayPort. I have not tested if Monterey 12.3 and Thunderbolt-3 or HDMI work better as my Thunderbolt-3 hub only has DisplayPort.

I suspect there is a regression in 4K monitor support in 12.3 over DisplayPort.

It would be great to hear from Apple what changed.

Interestingly, a direct Thunderbolt connection the monitor works fine without the crazy dimming issue introduced with 12.3.

This sucks. I have to buy new hardware a TB-3 cable or a new TB dock just because of a point/security MacOS update.

Just ridiculous

Same thing happening with mine. I have two external monitors via Thunderbolt to my 2018 intel Mac Mini. Everything was fine until I updated last night. Only one monitor with display after logging in. Safe Mode made no different, port swapping, cable swapping also did nothing. I called support and went through all the other 'fixes' they suggested and nothing worked. They basically shrugged their shoulders and said to wait until they release a fix or reinstall the OS - pretty **** drastic for something they broke.

If you are using display port and have the ability to switch to thunderport, this should get you working again.

I acknowledge this a not a solution but rather a mitigation if your monitor supports it until Apple fixes the issue.

If one can get into the computer and turn Off " Scaling " in System preferences >> Display how does it function then ?

Tried DP 1.1 to no joy.

I would love to hear from Apple how get this fixed.

I was not having this problem until I loaded the MacOS 12.3.1 update. I have not been able to get this resolved as of yet. Open to ideas...