To find interests outside gaming, just pick things that you think look interesting. You may end up not digging it. You may fucking love it. You just gotta try. In my 20s I went through loads of hobbies until I settled on the ones I enjoy the most.

Gaming imo isn't something you should quit. You enjoy it for reasons. You just spend excessive amount of time on it simply because there is nothing else going on for you. So you gotta do something. Right? But you don't want to watch movies or tv for hours on end because it doesn't engage your brain much like games would.

I enjoy the instant gratification gaming offers,

But you still have to spend time in a game to become good at it, nawimsain? Progressing along the learning curve is part of what's engaging about them. It's similar for most hobbies. And that feeling of gratification is also similar.

and I also find that becoming good at a game makes me feel better about my limitations in other areas of life.

Just like you'd use time to become good at a game, you can also use time to become good at a hobby that you end up liking. It will provide that same good feeling. Again, don't think of it as a replacement for gaming. But rather something else to enjoy on top of gaming.

For myself I love gaming. But I only really game for 2-4 hours a week. Occasionally I'll spend an entire Saturday in a game. Maybe once every month. It's my "people suck I want to be alone" time. And sometimes a game will draw me in for longer periods of time.

Another hobby I like is board gaming. Now, I happen to have a handful of friends who also love it. So we just play with each other once a month. However, if you are not so fortunate I would suggest looking for hobby stores or card stores or even nerd-oriented bars! They'll have board game nights. It's still gaming. But it's a change of pace for ya. It will get you to expand your social contacts too. Who may introduce you to other hobbies along the way.

I wouldn't recommend card games unless you have a steady source of income with enough leftover for hobby-spending. You say you currently play 12 hours a day so I have to assume you are only working part time, if that. That said, work more. It will let you explore more hobbies that might cost more.