Update: my mini fails to wake from sleep every 1 in 5 times and crashes, requiring a full reboot. This is as bad as when i picked up my mini in December 2018. Speechless....
Interestingly, there was a bug in Mojave that prevented my Mini going to sleep. It took a couple of months to be fixed but it did work. There was an associated BridgeOS crash.
Because I have a Mini and not a notebook, I had it disabled (the power-save sleep) for this reason.
In the evening, I just switch it off.
Haven't really tried with Bug Sur, TBH.