For fantasy TTRPGs, I can't express how fun Warhammer Fantasy RPG is to play and run. It's quite different to 5e, as you don't have a generic class, but rather a pretty specific job (such as being a rat catcher, town crier, caravan guard etc.). Definitely best suited for more grounded and gritty campaigns though!
Have you ever played any horror-focused TTRPGs? Call of Cthulhu is super fun, I've played that a few times. The other really niche one I am yet to play but really want to is called Dread: rather than using dice, you use a Jenga block tower, and big pivotal moments/actions make you play Jenga, and if you knock the tower over you die.
I know it might be a bit too 5e adjacent, but there are also some absolutely awesome conversions to other settings. SW5e turns 5e into Star Wars, which I've run two campaigns in previously and works really nicely. There's a similar conversion for Warcraft too, which is sick.