Learn a language. This basically morphs into other hobbies, like reading or listening to stuff. But it’s gratifying.

Video games - but a little different from other suggestions, get really deep into a game. Learning to play some games is a hobby in itself. Speedrun your favorite, get into your local fighting game scene or play Fightcade, get Slippi and play Melee online, go for high scores in some shmups, competitive Tetris or Puyo Puyo. Etc etc (Though re-reading op, I guess a lot of these may have unreasonable learning curves)