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)

Egyptian Mouse Pounce. Fun simple card game against cats I like to play to mindlessly pass the time.

Klondike Solitaire

(just kidding there are literally no good freecell or solitaire games on f-droid, go look I implore you!)

Luanti, Mindustry, vector pinball, super tux cart and Tux rider.

Honorable mention: Tailscale+Moonlight (game streaming)

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!