A smart powerplug and/or a fingerbot would solve that problem I guess? But at that point it’s probably cheaper to buy a network connected picture frame.

You could use something like the Toshiba flash air?

Systemd timer to poll upower when running on battery power, when battery is at 20%, use either system beep or set system volume and play a sound?

I use a single gpu that I detach from my host and reattach in a vm when I start the vm (and vice versa). I don’t think windows will enjoy a sudden lack of gpu.