|⇧ Position after 20...Qb7|
|⬇︎ Black resigned after 22.Rh3|
21.Rc3! leads to the quickest win. The weak spot in Black's camp is the h6 pawn, and there is little that Black can do to prevent White sacrificing a rook on that square and delivering a quick mate. The game finished 21...Nxe5 22.Rh3 and Black resigned. Capturing the bishop instead of the pawn would not have altered Black's fate.
21.Bxf8 is not as stylish but its still wins. Black can route his knight back to defend his king's position (using the e7 square), which delays (but doesn't quite stop) White's attack. With an exchange up, White can also win in more mundane ways, but once the manoever Rc3-h3 is spotted, winning the exchange becomes irrelevant.
Instead of 20...Qb7, Black could have tried 20...Rfc8 21.Bd6 (21.Rc3? Qxe5) Qd8 22.Rc3 Ne7 in order to preserve the exchange and get some help to his king (e.g. 23.Rh3 Ng8!).