my elo has stopped growing

I think you could just decide on a few openings that you normally use and study them, because in blitz openings are pretty important

Try playing slower time controls like 10 mins + 5 sec delay. Watch good videos on tactics from GothamChess or Chesskid's videos. Play lots of puzzles to improve your vision of the board (so you don't hang pieces) and to improve on those tactics. In addition, learn some good openings for black and white. For black, I play the Caro-Kann and for white, I play the Vienna. Both are great openings for beginners that really help with the tactics and is easy to learn.

Good luck on your chess journey, I believe you can excel if you really put the time into it

Honestly, i’m certainly no expert, but what helped me out a-lot at them levels was to learn some beginner opening traps off youtube videos. People always fall for them and that should be enough to carry you to 5-600. At that point start learning some openings, thats where i am at now anyway. Good luck!

Improving Your Chess - Resources for Beginners and Beyond.....

https://www.chess.com/blog/RussBell/improving-your-chess-resources-for-beginners-and-beyond

I've started watching a lot of content in youtube and lessons inside chess.com. seems to be working fine. Im also stuck in my elo (600 rapid, 500 blitz/bullet). I probably need to analyze my games and learn some theory. GL!

My ELO stopped already 20y ago

The games where you resign in a completely winning position might have something to do with it.

Example:

https://www.chess.com/game/live/113707771849?username=tyler_waldrop