Hello all,
I have had the same problem (and most of chess players). I had improved a lot in the beginning but eventually I hit a mental wall. I became frustrated and my rating started to decline. However, I found that my problem was in three things:
1. Behaviour habits while playing chess.
2. Analyze games in the correct way (no engine).
3. Middlegame strategy (pattern recognition).
Make sure that you only play serious games if you are in a good mood. I have found that if you play in a bad mood (especially after a bad loss), you can be affected and play poorly as a result
Also, analyzing games is a very important way to improve. Study grandmaster games from databases.
Lastly, it's all practice. If you do chess for a certain amount of time every day, and you make it habit, you will improve. Always remember that chess is fun, I discovered a fun YouTube channel recently that hopefully demonstrates this (and hopes receives more recognition!)
youtu.be/5aFKIG-Xt4Q?si=J4AchAlKziFSGutBBest of luck!