Most of my playtime is done on my smartphone when traveling by train to and from work. Mostly turn based strategy games. Magic the gathering Arena and Teamfight Tactics gets most of my playtime. But adventure games and visual novels also get a significant playtime on the go. Phoenix Wright and The walking Dead being prime examples.
I have tried a few action games but they do not work well for the format. I did like Diablo Immortal (everything pre-endgame is actually good) and I like several rough-like kill everything until you die type of games.
I have also played a few more artsy or philosophical games like Papers please and Paperclips. Not big experience but thoughtful experiences.
It is not the best platform for any game, but the convenience of it still rack up gaming hours.