i did a lot of puzzles and improved a lot really fast, but i think its not too easy after 1200 rating
How to improve fast

I agree, I've been approaching learning the same way you've mentioned and it seems to be working. I've been trying to play with the basic concepts in mind and learning from my mistakes after the game.

Hi! My name is Lauren Goodkind and I’m a respected chess coach and chess YouTuber based in California:
https://www.youtube.com/channel/UCP5SPSG_sWSYPjqJYMNwL_Q
It looks like you are serious about getting better at chess. Another idea that I have is to hire a coach. The coach can analyze your chess games and more. This is a great way to get better.
I wrote about my current thought process and how I'm approaching my chess journey.
I'd love to get some opinions from some higher rated players on whether this is a good idea and what I can add to my list to improve even faster.
https://www.chess.com/blog/lee0nerd0/how-to-get-better-at-chess-in-the-shortest-amount-of-time