I feel you, since I started getting back into chess 400 was my wall for a bit. now its 650-750. What helped was no joke this video series.
Building Habits
I heavily recommend you giving it a watch. The most important thing I took away from it is that while watching is how to go from opening to the middlegame better. ie the tip about how to use your rooks. It was a simple bit of advice that never sunk in till I saw the series. As well as the realization that people blunder ... alot. Especially at our level. So instead of crafting intricate plans just play good/decent moves that makes your position just a little bit stronger and wait for an opponent blunder. Then trade off pieces as fast as you can to simplify the position.
I'm stuck under 400 elo. At one point I thought I was getting better tell I got worse again. I'm playing 15 min games so I can slow down and think but still struggling with blunders. I did get better from 100 elo, my goal is to be 700 but it seems impossible. People are hard to beat around 400 elo can't win enough games to keep a score. Allot of the time I can't figure out what my opponent is trying to do to me before getting mated. I get outplayed ALLOT. I have gone the route of just defending pieces, controlling center ect the entire game but that just stagnates me with limited development tell my opponent breaks my pawn structure and moves in with knights for example. I'm reaching 700 games played over the past year. Chess has humbled me into feeling like an insect. I guess this is more of a self defeating rant lol.