agb2002: White has one pawn less.
White has five pieces to attack the black castle and several candidates, 23.Rxe4, 23.Nfxh6+, 23.Ngxh6+ and 23.Bxh6.
In the case of 23.Rxe4, eliminating the defender of f6, the queen is under attack after 23... dxe4, which may limit White's options.
In the case of 23.Nfxh6+:
A) 23... gxh6 24.Rxe4
A.1) 24... dxe4 25.Nf6+
A.1.a) 25... Kg7 26.Bxh6+
A.1.a.i) 26... Kxh6+ 27.Qh5+ Kg7 28.Qg5+ Kh8 29.Qg8#.
A.1.a.ii) 26... Kh8 27.Qf5 Qxf6 (else 28.Qh7#) 28.Qxf6+ Kg8 (or 28... Kh7) 29.Bxf8 K(R)xf8 (due to 30.Qg7#) 30.Qxc6 + - [Q+B vs R+N].
A.1.a.iii) 26... Kg6 27.Qg4+ Kxf6 (27... Kxh6 28.Qh5+ transposes to A.1.a.i) 28.Bg5+ Kg6(7) 29.Bxd8+ followed by 30.Bf6 + - [Q vs R+P] and attack.
A.1.b) 25... Qxf6 26.Qxf6 Re6 27.Qh4 +/ - to + - [Q vs R+N] and presumably a long fight ahead.
A.1.c) 25... Kh8 26.Qf5 seems to transpose to A.1.a or A.1.b.
A.2) 24... Bg7 25.Nxh6+ Bxh6 (25... Kf8 26.Qxf7#; 25... Kh7 26.Qf5+ Kh8 27.Nxf7+ Kg8 28.Nxd8 wins) 26.Rg4+ with a winning attack (26... Bg7 27.Bh6; 26... Kh7 27.Qxf7+ Kh8 28.Bxh6).
A.3) 24... Re6 seems to put up more resistance.
B) 23... Kh7 24.Qxf7 seems to win a pawn at least.
C) 23... Kh8 24.Nxf7+ followed by 25.Nxd8 wins.
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The defense in A.3 above, leads to reconsider 23.Rxe4 directly:
A) 23... dxe4 24.Nfxh6+
A.1) 24... gxh6 transposes to A.1 above.
A.2) 24... Kh8 25.Nxf7+ Kg8 26.Nxd8 exf3 27.Nxc6 wins B+N+P for a rook.
A.3) 24... Kh7 25.Qxf7
A.3.a) 25... Bd6(e7) 26.Qf5+ g6 27.Qf7+ Kh8 28.Bxc4 bxc4 29.Qxg6, with two pawns for the exchange and attack (threatens 30.Nf7#), looks winning.
A.3.b) 25... Qh4 26.Nf5 Qd8 27.Bg5 and the double threat Bxd8 and Nf6+ seems to win (27... Be7 28.Qxg7#).
A.3.c) 25... Re7 26.Nf6+ Kh8 27.Qg8#.
A.3.d) 25... Qe7 26.Qf5+
A.3.d.i) 26... g6 27.Nf6+ Kh8 (27... Kg7 28.Nxe8+ wins two pawns) 28.Qxg6 looks lost for Black.
A.3.d.ii) 26... Kh8 27.Nf7+ Kg8 28.Ng5 seems to win.
B) 23... d4 24.Ngxh6+ Kh7 (24... gxh6 25.Rg4+ and 26.Qxc6 + - [B]) 25.Nxf7 looks winning.
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