Mac mini 2018 boots to macOS installation

My 2018 Mac mini (i5/256/32, Sonoma 14.1.1) has been unplugged from mains power for about 24 hrs, and when I turned it on there was no chime and no video (using USB-C connection to LG monitor).

I tried several restarts and eventually the Apple symbol appeared - again, no chime - and I was presented with the macOS setup screen (choose language).

I notice that the Mini seems to be hotter than usual.

Booting with Cmd+R again gets the macOS install screen.

A bit more background: I have always connected my monitor via USB-C, but recently I wanted to use that port on the Mac, so I tried connecting my monitor via HDMI. Thereupon a sea of woe ... as in countless post to so many forums, including this one. I could only get the HDMI connection to work - sometimes - after first booting up with the monitor connected via USB-C, then plugging in HDMI. This would work UNTIL the Mac was powered down and unplugged from mains. Thereupon a sea of woe ...