Ghostwire: Tokyo is a good game about ghosts that's not actually that scary. The school DLC for it can get a bit creepy though. Also, Subnautica is one of the scariest non-horror games out there.
Ghostwire Tokyo felt like a pretty good length for an open world game. There were a bunch of relatively short side quests, and the usual collectibles but the whole thing was 100% complete in under 30 hours. Thier rougelike DLC add-on might push it over that, but it's basically a whole separate game.