I think it’s Qg3

… isn’t Q-f5! mate in 1? Edit: oh, it’s illegal, opens white king up to rook, nm

2nd try: bishop takes rook, black has to take bishop with rook, then Q-f3! Edit: no wait, crap, same issue as before, nm

Looked it up. Kept forgetting black couldn’t move their rook without exposing their king to the bishop

With the provided solution, couldn’t black survive longer by moving N-d3? They’re set up to take the rook that checks the king if white proceeds with that plan

Oh I see. That’s just a different mate. Fun interactivity