For oldschool shooter experience you can just install Quake Live from Steam. You won't have trouble finding active servers in it.

afps is pretty dead. there are a handful of people on qw, q2,q3 but if you don’t wanna dig around start with the microtransaction feature quake champions or the quake re release while people are playing it again.

also shout out to banana shooter or straftat if you want a quick fix in a f2p game. it’s not really afpsy but pretty fast movement and wacky guns in both