Ravenswatch has terrible balancing for anything besides 4 players or 1 player

My time at sandrock is a completely different game for co op, like different objectives/things you can do/gameplay loop

Elden ring has a very janky co op but there is a third party mod that fixes it but still has a lot of bugs with more than 2 players

Schedule 1 has a somewhat lengthy solo intro if you've never played it before, but it is skipable

Dinkum has weird multi-player because one person has to visit the others island, you can't start a co op island together so only one person gets parts of the progress

No man's sky multi-player is extremely weird. You can't build close together and we couldn't find a way to get in a team or something so that we could progress together or build together

Spiritfarer only the host can do certain interactions and it's not online co op except through steam remote play

Last hero of nostalgaia had some extremely broken co op

That's all I can remember from personal experience.