Linux Gaming

Rocket League. It has an outdated Linux port that still runs just fine, just no online play, then runs great in Proton, too.

So technically, it qualifies.

Space Station 14, seriously one of the best games I've played.

One of them would have to be Life is Strange 1, it's a pretty good port and honestly it's one of my fav games of all time.

Out of all the games that I know for sure that have a native Linux port, I'm either going with Minetest, which I have been playing for Voxel Libre (once Mineclone2), or the Sonic Robo Blast 2 with the Reveries mod, despite not knowing what exactly it changes. They're the 2 games I know have a native port that I've been playing the most recently.

My top answers are of course Kerbal Space Program, Dwarf Fortress and Stellaris.

However, all those have been mentioned already, so, to add something new to the list: Pathfinder: Kingmaker. It is currently my favourite cRPG.

Edit: Since you mentioned "Great Linux ports": Kingmaker has a game-breaking bug in the Linux version regarding Gamepad input. However, as long as you play it with mouse and keyboard (as the gods intended - insert PC Master Race meme), the Linux version is working perfectly fine. However, if you plan on playing it on the Steam Deck, you might want to play the Windows build.

The new Valheim update was pretty fun. I also like playing CS2

Open source, more modern, Ultima Online client. Still need the original art files. https://github.com/ClassicUO/ClassicUO