It Takes Two is probably the best jumping off point (as you’ve already been informed). It has enough variety that you can discuss what parts they liked and maybe find the games in that kind of genre.

My partner isn’t big on games, but loves The Binding of Isaac for coop. The latest DLC adds a better coop mode, but the original coop mode with coop babies works well too (and there’s advantages like them being able to fly so they don’t need to worry about floor hazards). I think the fact that they grew up in a catholic household but aren’t religious helped them get into it lol.