Borderlands series (Tiny Tina’s Wonderlands as well), Gunfire Reborn, Vermintide 2, Helldivers 2, Remnant: From the Ashes, Valheim (not fps but you can use mods for first person view) and coop is amazing in Valheim, Nioh 2. Also could do Gears series (3rd is best, 4th and 5th are ok but still decent fun with friends).

I’ve been into co-op games lately with my friends.

Edit: steam spring sales is coming soon™. Can’t wait to grab a few of those.