[Linux] Online games with active modding and mapping communities?

I've been missing the days of the 90s/early 2000s modding and mapping, specifically for FPS games - where you could go from playing Quake 1 to Team Fortress, or Half Life 1 to The Specialist. Complete overhauls that changed the game to something unrecognizable. Even maps - I loved rat maps where you were the size of a rat in, say, a kitchen - with dangers like hot stoves or rat rats.

I'm not necessarily looking for FPS games that do this, however I do want to enjoy the good ol' days of active modding communities, active mapping communities (Rat maps, jumping puzzles, Climb maps, conc maps, etc.), and just creativity in general.

The game(s) recommended don't have to be Linux-first, but should at least run in Proton.

Open to any and all suggestions!