I am not a fan of the new Fortnite social media combat games but good shooter games can still be fun especially if you are interacting with kids/teens.
I am a linux user and I like a fun free game that runs on old hardware but is still reasonably detailed.
Soldner Secret Wars is not pure, it is a win32 game so you need wine to get compatibility and it requires a x86 or amd64 machine to run but it is free and there is no copyright/pay/legal issues, the company turned it over to a community to maintain both the bins and online clan hosted server software.
So if you like a team pvp game with some realism like blowing up terrain and a pretty comprehensive realistic armaments inventory form submarines to rifles to fighters give it a try.
Also pass the links on to nerdy kids as a superior free alternative to get them off of the Fortnite and PubBG pay for wagon.
http://soldnersecretwars.de/
https://en.wikipedia.org/wiki/S%C3%B6ldner:_Secret_Wars