MMO but singleplayer? Thousands of hours of content?? Super grindy?

I need numbers go up game /turn your brain off MMO style

I'm looking for games where you unlock skills and character abilities.

Games I've played Poe 1 and 2, Warframe, first descendants, way finder, last epoch I think nioh 2 counts as well.

(Would prefer stuff that don't require playing with other people)

(I really enjoyed Witcher 3 and cyberpunk 2077 (unfornately don't like monster hunter)