I'm tired of the pain.

AND I AM PAIN

learn opening theory from channel named "Hanging pawns"

If ur looking for a new hobby, i recommend you keep playing chess, but before and after, do something relaxing.

<<I picked rapid time controls and some openings, and I stuck to them. I started doing tactics puzzles that I could accept doing.>>

You're not improving perhaps because you made three mistakes (above) thinking they were the right things to do.

You should play rapidplay but also slow classical controls. You should NOT stick to the same openings when you're learning. And tactics puzzles are best left until you can already play quite well. They will hinder your improvement as a beginner because they program your mind wrongly. In puzzles, you know there';s a solution. That's bad.

Also, something else you wrote shows that you do not get a good feeling from playing well. You only get a good feeling from winning. That's the wrong attitude because you should be trying to play well when you learn. Otherwise, what's the point?

Do an experiment, play chess at different times of day and observe when you play best (or think you do), play mostly at or around this time. You could also treat positions as puzzles where you either try to win material, get a positional advantage, or find a mating net/checkmate, etc.

Are desktop or mobile, if desktop, draw arrows (with different colors if you want) to help with calculation, if mobile, the try to put a real board to use to help calculate by playing candidate moves on the board.

dont play right after u eat

This sounds weird, but its true trust me

I bought Levi Roadman's Hoe Toe Won It Cheese.
He better appreciate it!
Or Not.

You got a lot of blood flow to digestion after eating, it makes sense.

Similar to the OP, having put a significant investment of time and resources into chess over several years - just wasn't improving. Likewise, I'd thoroughly learn some aspect of chess with the promise of 100+ improvement, only to then go backwards by 100+. I don't have the temperament for chess particularly OTB chess. After losing long games after a 2-hour grind or due to some atrocious blunder (of which I too often make despite how hard I try not to) at evening chess club I would drive home seething at my incompetence, almost feeling my blood boiling, then literally have sleepless nights! Nowadays I just play on here 5 minute for fun and 3 day correspondence for some kind of deeper chess application, and am finding the losses aren't overly affecting me beyond say, a few minutes after any one game. I have other hobbies which I (unlike chess) I do experience improvement with application and practice.