It's not exactly indie, but on Linux I can't play Fortnite, so anime knockoff Fate Trigger has been fun to try out. It uses hero shooter abilities, and has a very fast time to kill, while also being third-person, which I suppose is a combination of factors we don't see much (I guess maybe it's close to PUBG, but I've never played that. One differentiator there is the characters being colorful, and environments low-poly, which makes people easy to spot).
I played Ground Zero on the last nextfest. It's fun, but hard as far as survival horror goes. It has unique mechanics for shooting and for defending that give a lot of skill expression, but it means if you're not using them well you may become starved for ammo.
Pragmata, from Capcom, also seems to have some unique shooting mechanics, but you go against slightly slower, more digestible enemies. I enjoyed the demo, short as it was.
Far Far West was fun, but given that it competes in the same spheres as games like Helldivers, it's a little hard to recommend against more established games.