b5+!, cxb5, Kb4 and zugzwang. Just make sure not to stalemate black. If f6/f5, then exf6, exf6, e4, f5, e5! (Taking is stalemate and thus a blunder), f4, e6, f3, e7, f2, e8=Q, f1=Q, Qxb5#. Black has other options but they involve not queening and white just letting the king escape at the right time and queening.
Thank you so much for this detailed comment! It’s not a position I want to be in…I wonder what had to happen beforehand for black to get themselves into this mess! Pretty wild middle game!
