Squad from Offworld is a tactical first-person shooter that has run on Linux for a while now with Proton, but some Linux distributions had issues with Easy Anti-Cheat (EAC).
Squad is an awesome game, and I've played hundreds of hours on Proton. However, unless performance has drastically improved since last December, I would not recommend trying to play it on Steam Deck. I got about 20fps, with regular and significant drops. It is a seriously good game though for those who like a good tactical multiplayer shooter. OWI also makes a Starship Troopers game and Squad 44 (sort of a WW2 version of Squad but different, does not run on Proton due to EAC) so I hope they get the same treatment.