Alto’s Adventure is a pretty chill game to play when killing time. https://play.google.com/store/apps/details?id=com.noodlecake.altosadventure
I also like the “connect the dots” puzzle games, like this one: https://play.google.com/store/apps/details?id=com.playvalve.connect.dots
Neither game requires microtransactions for the full experience. They might have ads, but my adblocker blocks them if they do.
To run a service outside the user context, probably.