For me, it would have to be something nice, but not so interesting that I want to stay awake (Ariadne auf Naxos). Or something I’ve heard a million times (The Magic Flute).
Beethoven has always been calming for me, so maybe Fidelio too.
If you’re looking for beautiful music, maybe Tosca or Rusalka.
There are others that I wouldn’t necessarily fall asleep to, like Don Carlo, Pagliacci, Rigoletto, or La Traviata. This is a pretty good list of some of the best known operas.
I started learning a little about music theory. I’ve been interested for a while, but always thought I wouldn’t be able to understand it. But it’s doable, a little at a time.
And I’ve been going outside more. I spend too much time in front of the computer. It’s nice to have fresh air and read, listen to music, or just take in the surroundings.