I have a late 2021 unibody Mac Mini, upgraded to Catalina. For some time I have had problems where the monitor will not wake up from sleep even though the Mac is running - I think it's a known bug in the hardware/firmware.
Recently I thought I had solved this buy setting the screen to never turn off:
I thought it was working but recently I am coming back to my Mac after several hours and frequently I turn the monitor on with its own power button to find the same problem. Every time I have to hard reboot the thing.
How can the screen still be put to sleep when told not to? How can I prevent it?