easy!!!
Hardest Mate in 1

This the hardest mate in 1 I can find. There is only one mate in 1 and it is White to Move. This is incredibly hard!
I must remember this motif next time I have two queens and four bishops on the board :-P
Fun exercise though.

Bruh it's clearly d8Q how is this a debate? Qa3 can be blocked by Qc5
But the quuen is pinned

No one could replicate the game or even the final position, so it means that there is no proof, a real proof, what is the checkmate. It means that this puzzle was actually a joke made by a senior GM and that is why no one recreated the board.

thats not mate in 1, mate in 2
I think it is "Qa3#".