Some of my favorites:

1. https://tangramgames.itch.io/tobu-tobu-girl-deluxe A more GBC classic game that was made somewhat recently. Its deceptively hard but has very tight controls. The music is fantastic and makes me want to get good at the game just to hear a bit more of it.
2. https://www.wesnoth.org/ I love this game. Im not very good at it, but its super fun and open source. Runs on just about anything. I got it working on a Miyoo mini plus of all things once. Its a strategy hex game.
3. Pokemon hacks - Theres a metric ton of these. But Ive had fun with Pokemon Unbound recently. It feels like a completely new game.