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I'll have to give this a try. I am not using my 2021 MacBook Pro as a desktop anymore because of

  1. Excessive RAM usage with external monitors
  2. Black screen for a few seconds intermittently
It's been running fine as just a laptop though. I still think that there are memory leaks as RAM starts at about 14 GB and just keeps creeping higher to about 22 GB (the rest is cache), and then I usually reboot it when it gets there. I don't see why it just creeps up but I only reboot every ten days or so. 12.3 has actually been the best Monterey for RAM issues. I found a different solution for the desktop (cheap, used iMacs) but I will test out 12.3 with external monitors this weekend to see how they do. I did buy better cables as well but I never tested them on the MacBook Pro because of the other desktop solution.
 
For me 12.3 is worse than 12.2.1 ... Can't connect my 2 external displays anymore with a thunderbolt 3 dock (likely the DisplayPort problem, reported here on Macrumors) and if I let my MacBook Pro 14 sleep for a while it won't reconnect to one of the external displays connected through USB-C. I have to reconnect it ...
Oh and since 12.3 external drives connected through the thunderbolt 3 dock are disconnected without reason when the Mac goes to sleep (had this problem before with 12.1). So keep your eyes open for data-loss!
 
I hooked my 2021 MacBook Pro, running 12.3 up to a Dell Ultrasharp 4k USB-C monitor, U2720Q via a Belkin Thunderbolt3 Cable (USB-C to USB-C), 100 Watts, 0.5 meters). I experimented with sleep playing around on the deskopt, virtual desktop and observed no problems with blackouts or the external monitor waking up from sleep. I think that I ordered this particular cable when I had the blackout problems using other cables.

I then tested using a Cable Matters USB-C to DisplayPort 1.4 Cable Supporting 8K 60 Hz 6 ft, Thunderbolt 4/USB4/Thunderbolt 3 compatible and this worked as well. The computer and monitor were the same. It did take 3-4 seconds for the monitor to wake from sleep but this is normal.

I have had black monitor issues since July 2021 with my M1 mini running Big Sur and with the 2021 MacBook Pro 16 but I think that all of these problems were resolved with upgraded cables. I do not recall any black monitor problems with the mini since using the upgraded cables.

I think that I bought them because of discussions about black monitor problems on the Apple Silicon forum. I do recall black monitor problems when I received the MacBook Pro last fall but I think that the USB-C cable worked when it arrived. I may have had problems with the HDMI cable. Apple Silicon Macs do seem picky about cables.

I am unable to test dual 4k external displays as my extra displays are on another table with one currently hooked up to another computer. But I think that this test is sufficient for me for my configuration. I do not plan to use the laptop with external monitors though - it's just being used standalone for now.
 
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