Rb3+

Hello, this is a game i recently played. I was analising the game and if black plays 52. b5 (instead of c4) and white plays 53. Rxh6,
engame table shows only one move as winning for black; Rb3+. Can anyone explain to me what makes this move better than playing c4 instead? I'm having a hard time with it. Thank you.

52... c4 is premature as white holds back the pawns with 53 Rxh6 and 54 Rc6 and then advances his own pawn with 55 g5.
The check 52...Rb3+ gains a tempo as the rook controls square c3 to advance pawn c5-c4-c3.

Thank you, it's clearer now.

I think it's also completely fine to play b5 - you need to advance the pawns in tandem in order to protect each other. The b pawn is already protected by the rook and further from the opponent King, so it's a better one to advance first.

Yes 52...b5 53 Rxh6 Rb3+ transposes and wins as well. It is essential to give the check 52 or 53 ...Rb3+ to win a tempo.