Retro arch/ any emulator is great for this. I can waste an hour on 1st gen Pokémon on short downtimes. And when im stuck in layover or on the train, I can crank out half the story of chrono trigger.
Start retroarch > press load core > choose download core and download desired core(they’re organized alphabetically so scroll down for nintendo, sony consoles etc.) > press load content to browse your phone memory for the game you wanted to play.
^Above steps are only needed the first time.
*If you’re confused about which core to choose you may find this handy in helping you choose the best option(or learn anything about emulators really).