agb2002: The pin suggests e5-Ne4 and Nf4-Nc(f)d5.
In the case of 21.e5 Qxe5 (21... dxe5 22.Ne4 wins a piece) 22.f4:
A) 22... Qe3 23.f5 Qe5 24.fxg6 Re6 25.gxf7+ looks very bad for Black.
B) 22... Qe6 23.f5 Qe5 (23... gxf5 24.Rxf5 wins decisive material due to the pin) 24.fxg6 as in A.
C) 22... Qe7 23.Ne4 wins decisive material.
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In the case of 21.Nf4 Qe5 (21... h6 22.Bxh6 wins a pawn) 22.Nfd5:
A) 22... Re6 23.f4 Qd4 24.Rcd1 Qe3 25.Rf3 traps the queen.
B) 22... Nfxd5 23.Nxd5
B.1) 23... Nxd5 24.Bxd8 seems to win an exchange.
B.2) 23... Ra8 24.Nc7 wins an exchange.
B.3) 23... Rb8 24.Nf6+ Bxf6 25.Bxf6 weakens the black castle seriously.
B.4) 23... Rc8 24.Nf6+ as above (24.Ne7+ Rxe7 25.Bxe7 f6 traps the bishop).
C) 22... Nbxd5 23.Nxd5 Re6 (23... Nxd5 as in B.1) 24.f4 Qd4 25.f5 (or perhaps 25.Rcd1 Qb2 26.f5) 25... gxf5 26.exf5 Qxh4 27.Bxh4 Re5 28.Bxf6 Bxf6 29.Nxf6+ wins decisive material.
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21.e5 looks considerably stronger than 21.Nf4.