gaming on Linux has come a long way, proton is great and can be used outside of steam, like with Lutris or Heroic Launcher

The COD2 single-player campaign is good. Any of the boomer shooters like Doom, System Shock. Far Cry, Arma, maybe UT.

https://www.gog.com/en/games?genres=shooter&tags=tactical&order=desc%3Abestselling

City Connection, Bugs Bunny’s Crazy Castle. While neither are co-op my mom and took turns playing crazy castle on the nes when I was a kid and we beat it. Core memory right there.

I think Tetris or Doctor Mario had 2 player modes but I’m not sure.

Does Sonic Spinball on the Genesis have multiplayer?

I don’t even boot windows anymore and it still takes over the first boot spot randomly.