I use a Mac mini 2018 intel for design work. After updating to Monterey 12.3.1 I lost use of my 2nd display that is connected via HDMI cable. The display connected by USBc does still work. I switched the wires and the same thing, only USBc connection worked. It is not a problem with the monitors it is caused by the upgrade. I spent multiple days talking to multiple apple support advisors, even the ones at the highest level and no one was able to fix this problem.
If you are able, downgrade to Catalina. I was able to do this by backing up my computer first on an external hard drive. Then deleting the hard drive so it reverts to manufacturing settings. I was on MacOS Mojave 10.14.6 and the problem goes away. Then I upgraded to Catalina and my 2 displays were still connecting. My mistake was upgrading to Big Sur like the apple supporter advised me to do. Once I upgraded to Big Sur my 2nd display was not connecting again. This was the original problem. I figured I can go back and repeat my steps and stop at Catalina, but for some reason (no one could help) I was not able to. I kept only getting the option to download Monterey which was the original OS that caused the problem. So I am stuck only using only one display.
The only advise I was given was to talk to the manufacturer of the displays to see if there are any updates to the drivers available. That's right, blame it on the displays that aren't mac.