I run a 2018 Mac Mini with two Dell screens. Normally works really well as a setup. I had problems since updating to 12.3 in that only the screen attached by HDMI worked. After a number of restarts, checking wires, moving things around the solution was a PRAM reset, which on a Mac Mini is uplug it for a few seconds then reboot. Both screens now working fine. I hope this is helpful. thanks.