Semi-casual games that run well on older PCs and linux? Plus no launchers? Let’s see. I got a few but there may be splitscreen ones in this list too. (If that’s ok)

Battleblock Theater Biped (maybe?) Cassette Beasts Castle Crashers Children of Morta Don’t Starve Together Dinkum (If Australian Animal Crossing sounds interesting) Factorio A hat in time Guacamelee Human Fall Flat Hyper Light Drifter ibb & obb KeyWe Kingdom Two Crowns Knights and Bikes Like, all of the lego games (They’re all similar mechanically, so pick one of the newer ones that look good) Lovers in a dangerous spacetime Magicka (I like the first one but the second one isn’t bad) Monaco Moon Hunters Necesse Peak Resident Evil 5/6 (Yes, really, its a great time in co-op) Satisfactory Secrets of Grindea Split Fiction (This one may be graphically harder to run?) Stardew Valley Spiritfarer Terraria Trine games Valheim (At least until mistlands)

I’m kind of going off of semi-casual meaning not high intensity shooters or things that require crazy skills. Most of these are pretty easy to pick up and are generally forgiving. They shouldn’t have launchers but if they added one in a later update, then dang.