I really liked Flowit. I wish there were more of it (tho admittedly when I go back to it, I have often forgotten enough that it’s fun again)

Shattered Pixel Dungeon, popular roguelike (as in, actually like Rogue)

Mindustry, factory based sandbox tower defense (mobile Factorio)

Unciv, 4x civilization game.

Apotris is probably the best version if tetris available, and it’s foss.

You can get a compiled ROM for GBA and play it on android with a FOSS emulator like Lemuroid. It works!