I do blunders almost every game

How can I think 5 moves ahead if I cannot see everything in a single one? In one game its pretty ok, engine rates me as a 2100 player, next one I lose my queen for free, and it says I am 950. I know all the chess theory and it helps me nothing in blitz.

Do you use notation when you think about moves? I don't, I just do the moves, maybe that's the reason but idk, maybe my brain is just not compatible with this game at all.

It takes a lot of practice to calculate and visualize the board after your imagined move. That part is definitely no fun. It will become a little easier over time, like exercising any muscle.

I guess it is a difference between grokking and knowing. "Knowing chess theory" is not enough. You need to grok it and that requires a lot of drills and practice.

I guess experience and practice are not the case, I play some chess since the first Chessmaster games, and I think have played something about 50k chess games in my life or maybe much more idk, and I just can't get any better, I always blunder and I am forever stuck in ELO 1100-1300, it's like always on the beginner level, if someone else would put so much time in chess he would be easily above ELO 2000 already.

I don't know what grok means.

If blitz is your main time control, then I would suggest doing some rapid time control. When you do puzzle rush do 5 minutes instead of survival. When you say blundering then I am assuming it is mainly a tactical combo or hanging a piece, pawn or queen. Rapid will train your brain to draw arrows around the board in your head, so you won't blunder pieces as often and puzzles will train your tactics. If you are already doing this then idk what the problem is.

I don't think you can 'absorb it', you can't just learn to calculate quicker and more precisely, can you? I am not 800sh, I have been rated mostly over 1800 on other chess sites, but I was younger and my brain was better back then, today I struggle to get to 1300, maybe this is just what getting old is. Time to die people, nothing to see here, move along.

As you are speaking of ratings you had on other sites, those are not directly comparable.

For example, having a rating that is a couple hundred points lower here than on Lichess, is completely normal, as these are different rating pools. At least that is the case a couple hundred points below/above Lichess 1500.

Now knowing all the theory, do you mean you know all the opening theory? That is very hard to believe, but if so, maybe you want to spend more time studying annotated master games, chess strategy and endgames instead of opening theory. I think those should be more useful than just memorizing openings.

And I am sure you do not know everything about chess there is to learn. No one knows everything about pawn structures, endgames, common middle game plans and so on. Not even the world champions.

Of course, I do not know all the openings, but I know the most popular ones and all the end-game theory, I did hundreds of hours with J.Waitzkin and Larry Christian's academies and famous games analysis in the Chessmaster series.

My point was that I don't know how to even apply that to blitz or even rapid, people often do some crazy things that are out of the books, they violate all the rules ie moving the queen too much, yet they can beat me cause they just calculate better, faster and deeper, I try to catch up and then I'm blundering and losing pieces for free. So, I guess knowing rules and theories won't help you if someone is just more intelligent mathematically, you could watch all the tutorials like Gotham chess vids on the yt and all the games of some pro and it won't help you to improve your calculations, I think we are mainly born with our limits, ie I can't visualize entire board in my head, even without pieces I am forgetting some of the colors of the squares and have to re-calculate it, so I always terribly struggle with playing blind, while some 6yo kids can do it without even learning.