There are some community-server FPSes on here, albeit:

• The conversation thread is five years old.

• They won’t be discussing Linux functionality, as it’s not Linux-specific. Could be some sort of anticheat compatibility issue with them; would need to confirm.

https://www.reddit.com/r/pcgaming/comments/fuk1gb/are_there_any_modernish_fps_games_that_still_have/