I’m not even a huge platformer guy, but Rayman Legends is absolute peak and a fantastic, chill co-op game. The music levels in particular - where the already great soundtrack is synced in time to your jumps and hits - are incredibly satisfying and so well made.

I’d also be remiss if I didn’t suggest Blue Prince. It’s not co-op per se as it’d only be one person at a time “driving”, but the game is about puzzle solving so who holds the controller doesn’t really matter. It’s a fantastic game if you enjoy puzzles and escape rooms. My sister isn’t even a gamer at all but I recommended it to her fiancé and they’ve been playing together and even she’s been enjoying it a lot. From my own experience playing it on my own I also think it would be much more fun if playing alongside someone else. I’ve often missed having someone to bounce ideas off when stuck.