Very good move: practically forces the queens off. If 21...Qf7 22.Bd6 etc. It's pretty much game over from here on. All Black can do is the best he can and hope White loses the thread.

In principle, these piece exchanges aren't in Black's interest, given the material deficit, but in order to gain some kind of freedom, he has to submit to a simplification. White has used his material advantage to good effect, establishing a powerful bind on Black's game. Maybe Black ought now (or very shortly) to have begun pushing his centre pawns to free up his poor bishop at least.

(!)

Possibly Black ought at move 29 to have put the question to White: "If I play 29...Rda8 what would be your response?" Clearly White is planning 30.Rb6, but if 29...Rda8 30.Rb6 Rxb6! and Black is back! Of course, White might well have already prepared one of two good responses to 29...Rda8: 30.Bc7 or 30.Rb8ch...

I disagree on the winning move   If i would be black and clearly behind like this. I would play 32. Rxc3 resulting in 33. Rxc3 Rxa7 34. ( possible next moves 34. Bb8 Ra1+ The game is far from over black is behind but the game is drawable

A pretty good example of how to exploit a winning material edge. Black was never allowed so much as a sniff of counterplay once the b-pawn was lost...