Morphy v The French (part two)

THE second time Paul Morphy faced the French was in his 1858 match against Johann Löwenthal.
Morphy - Johann Löwenthal
Game 10
1.e4 e6 2.d4 d5 3.exd5 exd5 4.Nf3 Nf6 5.Bd3 Bd6 6.0-0 0-0 7.Nc3
So far exactly as in Morphy's Paris game against Chamouillet & Allies, who played the aggressive 7...c5?!, which soon led to Black falling well behind in development.
7...c6
Much calmer, and it has been one of the choices of strong modern players. Löwenthal commented in Morphy's Games Of Chess: "Most authorities recommend ...h6 here, but no disadvantage seems attendant on the move adopted in the text." 7...h6 was played by Judit Polgar in a short draw against her sister Sofia in 1989.
8.Bg5 h6 9.Bh4 Bg4 10.h3 Bxf3!?
Giving up the bishop-pair is a very committal decision, but note that Black keeps his better bishop.
11.Qxf3 Nbd7 12.Bf5 Qc7 13.Rae1 Rae8 14.Re3 Bf4 15.Re2 Rxe2 16.Nxe2 Bd6 17.Bxd7!?
Giving back the bishop-pair in order to try to gain an initiative against Black's king.
17...Nxd7 18.Ng3!?
Löwenthal: "A very good conception. The object of this move was to plant the knight at f5, where its action, combined with that of the queen, becomes most threatening and formidable."

How should Black meet White's threat?

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18...Re8
Löwenthal: "Black dare not attempt to gain the bishop by 18...g5, on account of White's playing 19.Nf5, menacing mate in two moves if the pawn captures the bishop. The move actually made was a good one as it secured a free range for the rook."
Stockfish10 and Komodo9 agree with Löwenthal's assessment, but they also reckon 18...g6 is good.
19.Nf5 Nf8 20.Bg3
Löwenthal: "The best possible play."
20...Bxg3 21.fxg3!? Re4 22.c3 Nh7 23.h4 h5
Löwenthal: "A weak move. It was not likely that Mr Morphy would take the pawn with queen, seeing that such capture would cost him the knight." Nevertheless, the engines reckon the position after 23...h5 is dead equal.
24.c4
Löwenthal: "This is a very strong move, and gives White the advantage."
24...Nf6?
The engines reckon Black is fine after a simple queen move such as 24...Qd7 or 24...Qd8.
25.Nxg7! (1-0, 34 moves)