The issues appear to prevent users from waking up a third-party display from sleep. It affects many monitors that are connected through HDMI and Thunderbolt and the only solutions are to disable the Mac mini from entering sleep mode or removing the display cable and plugging it back in again.
One user quoted that “the computer wakes the monitor but it fails to send a video signal” and another suggested they have attempted to resolve the problem “with 2 different displays with 2 different HDMI cables”.
Apple is apparently aware of the issue but hasn’t confirmed if a fix is on the way. It has also been looking into a display issue on the M1 Mac mini that causes pink squares to appear.