If the plan of f3 and e4 is effective enough to shut down the bishop on h7 then one might say that the novelty played by Nakamura is bad. I think his real problem was not playing the more active defense shown in the notes to black's 21st move. Note even in that line f3 and e4 are still possilble.
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rn1q1rk1/1pp2pp1/4pb1p/p7/P2Pb3/5NP1/1P1NPPBP/R1QR2K1 b - - 0 15
15. ... Bh7 {the novelty}
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r4rk1/1q2bppb/n1B1p2p/p3N3/P2P4/2Q3P1/1P2PP1P/R2R2K1 b - - 0 21
21. ...Qc7{the weak move}
"Good decisions come from experience, and experience comes from bad decisions."
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Ted Summers