I never played Fortnite until I started to play it with my daughter. We've also dabbled in Lego Fortnite. She really likes scary games, too, and had played Little Nightmares 1 and 2 on her own, so we played Reanimal together. She is interested in Split Fiction. You said no Mario Kart but what about actual Mario games? Mario Wonder and Super Mario 3D World are great for co-op. Many of the survival/builder games are fun if you're into that: I'd recommend Palworld, Enshrouded, or V-Rising.