What went wrong

I assume it would be better if you didn't move your king away from the e6 square, and your bishop from the e8-a4 diagonal, and it would be easy draw. Opposite colored bishops are often easy drawish, if your king and bishop are working together defending against opponent's pawns

check the time

Nice game
My perspective as a more beginner is you both try to keep the tension and miss chances to trade and just make it a draw. Both try to win in a very drawish position. As a result it’s easy to miss moves like trades or 36….f4!

it’s hard to see it’s so strong because it breaks a principle in pawn structures but it looks like some zugzwang and even though it’s opposite color bishops

you could win potentially all of white pawns on the kingside

I had LESS than a minute to play and I BARELY got into a drawn endgame before blundering. Although, from this game I learnt that thinking about your moves is the eigth deadly sin of chess, which impedes your progress. I didn't realize this so I was stuck below 2050, but after another game like this, I realized that thinking was the reason I was constantly losing games, so I stopped and I reached 2070-2080. I even crossed 2100! But it seems like this bad habit/desire of thinking about the position constantly is coming to me again.

No matter what the time situation is, 61. - Kf5 is insane. You can premove Ba4-Bd7 back-and-forth, and you can't lose. Why would you want to make a random king move?

I didn't have enough time to establish the fact that the fortress is of moving the bishop back and forth. I would've found the mechanism if I had a few seconds. But this comes from the problem of spending time on moves.

Okay then, so next time manage time properly.

If you already knew the answer, what is the purpose of this thread?

I needed more feedback on the opening and middlgame, but it seemed like everyone just jumped to the endgame. [ps: I just realized that the game started of in an endgame but I meant the early parts of it.]

It's hard to figure out that you meant to discuss the middle game when the title of the thread is "What went wrong".

As you probably already know, the endgame is equal, then out of the blue you were completely winning, but 36. - g4 loses a pawn instead of winning one. Obviously the answer cant be anything before that point.