What was my mistake on this game

first off I think you were slightly better in the middle game after that tactic of Bxe2 stuff, however, I'm not really a  huge fan of the move 22... e4 right away, I would have played a move like f6 first or something then if he attacks the bishop with like 23. Re3 then you can play just e4 and make him waste a tempo. on move 27 I'm confident taking the pawn wasn't a good idea because you have a lot of pressure on him with those two centers pawns, but taking the pawn on f3 just made his life way easier because he was able to trade pieces(a rook for rook) and improve his own pawn structure. finally, without even looking at a computer analysis, I can say white is better in the endgame. yes you do have a passed pawn, but your opponent has a way better overall pawn structure(all his pawns are connected while a lot of yours are isolated) and a more active king(while yours is in the corner doing nothing).

hope this helps!

A surprisingly well played first half of the game by both players. Because of the ratings I thought it would not be that good.

In the endgame you didn't play well though. In the opening we're taught to get our knights, bishops, and rooks active as fast as possible, because when lines open (when pawns are traded) the side with more active pieces will be better. Once lines open you no longer have time to bring your pieces into the game because the action has already started. Advancing pawns without strong pieces will just make them weak.

I bring this up because it's actually true all game long, not just in the opening. Your move 22...e4 was good, but it was also risky. It's a far advanced pawn when your pieces are not yet organized. When white played the f3 pawn break your pieces were about as disorganized as white's (doubling rooks on the g file was a waste of time). The good thing about your e4 pawn was it restricted white's bishop and knight. So when you captured on f3 that was a really big mistake. This let white trade off some of his bad pieces and it made your f and d pawns isolated pawns and weak and now lines have been opened and your pieces weren't ready for it. Instead of capturing on f3 you needed to play f5 to support the pawn and then work to activate your other pieces.

So if rooks on the g file were useless and I'm telling you to activate your pieces what do I mean? Well endgames are usually not about attacking the king. In this endgame your big advantage is your central pawns and in particular the passed d pawn. You need to support those pawns and not lose control of the squares in front of them (meaning don't let white blockade them). This is another reason why the move 22...e4 was risky, because you gave up the ability to protect d4 with a pawn, so white has better blockading prospects.

Anyway, after supporting those pawns white will find it very hard to, for example, move the bishop off of d1. Then you can slowly work to activate your rooks and king. If at that point you're not winning yet, then you look around for pawn breaks like a5 or h4, but this would be after 10 or 20 moves of preparation.

Anyway, 23...Rdg8 was bad because the endgame is not about checkmate, and 27...exf was bad because it gave up your strong pawn center and let white's pieces come out.

In the game after 34.Rxd1 white is almost winning. Whites rook is better, white's king is better, and d5 is the most vulnerable pawn on the board. In the endgame you need your pieces to attack enemy pawns. Moves like 31...Rd8 show you have a very wrong idea, this was a passive move. That's why I say white's rook is better, it's attacking your d pawn, and your rook is a passive defender of the d pawn. (If your pawn were on d3 or d2, then your rook wouldn't be so obstructed, and it would be doing a good job, but notice after 31...Rd8 your rook has only 2 forward squares).

Ok, well I think I've talked long enough. It was a really good first half of the game, I was surprised, but in the endgame it seemed you didn't know how to give your pieces useful jobs, and then 27...exf let white's pieces come to life and you were left trying to defend vulnerable pawns.

Yeah I was thinking the same thing, 22...f6 instead of 22...e4.

But his e4 + Nd4 setup was pretty interesting from a restriction point of view. White's d1 bishop was practically dominated, having  (more or less) no free squares. If black can hold that formation while activating the rooks I can imagine how it might win.