I think FOSS is uniquely awful for game development. I applaud anyone willing to donate their time but when it comes to games I much prefer pay-once as an attribute to focus on.

Game devs need to eat and donations are unreliable (I used to help run a community funded MUD - we admins often ended up paying server costs out of pocket) so I focus more on finding good games that avoid ad or microtransaction based revenue models so the most reliably good games I find are either shareware/demo before you buy or just a straight up cost.

I definitely appreciate OSS games though and there are good non-free OSS games out there, most people aren't dicks that reshare the source after purchase.

Vector pinball is quite fun, if a bit simple

Mindustry.

I think Anuto TD (a tower defense game) is the best I've come across.

I also really like Gauguin (Sudoku-esque) and Lexica (word game) on the more casual side.

Don't know that it's on F-Droid, but Lichess is also high quality and open source.

Endless sky is a spaceship sim that I started playing recently. It's well done, and there are a bunch of mods available for more story, ships, etc.

Endless Sky

Stone Soup Dungeon

the ones i play most often are Forkyz and Simon Tatham's Puzzles.

If you like Shattered Pixel Dungeon, there's also Dungeon Crawl Stone Soup on F-droid.

Space Trader

Open Flood (puzzle game)

AAAAXY is interesting for a weird mindfuck puzzle platformer.

Super Metro Mega Wars

Anuto TD

I've made a small foss shoot 'em up with bevy and plan on porting it to android at some point

Frozen Bubble is a solid Puzzle Bobble clone

TuxCart is pretty good!

Cards With Cats is a solid Hearts game.

PySolFC is a slightly clunky but workable solitaire.

I love Lexica, a word game similar to Boggle.

Finally, CrossWords is a good scrabble clone, though I've had issues with network multiplayer buggering itself. Good for local play still.

Freeblocks Pixel wheels

And retroarch

Shattered dungeon