Solution - and congrats to the winner of this round, Hive account@juanmi96!

The winning move is 1. Ne3!
Then black has several options:

a) 1. ... Qxe3
2. d8N! and black is lost. However, 2. d8Q loses because of 2. ... Kg5!.

b) 1. ... Rxe3
2. d8N! with a similar situation like in variation a): black is lost.

c) 1. ... Re1
2. Rh2! The only winning move. 2. ... a1Q (Moves like 2. ... Qg1 with idea to play Qxh2+, and then Rh1+, followed by a1Q+, only delay the loss.)
3. d8N! and black is lost.

d) 1. ... Qe1
2. Rxe1 Rxe1
3. Ng4+! Kg5! That's the best defense. After 3. ... hxg4+ 4. Kxg4 a1Q 5. d8Q black can't prevent the checkmate at h8 anymore.
4. Nh2! Again the only winning move as black has no check at h1 now. 4. ... a1Q
5. d8N! Again black has no more useful defense against 6. Nf7+, and can only delay the loss by several useless piece sacrifices.