Why ..h4 after h5?

Why does engine suggest black to play ..h5 after white played h4? I see this pattern often play by masters. Isn't this giving white knight a free g5 quare to conquer, move freely and disturbing the area later in the future? Also why are you scared of g4 push by white later?

6k1/1pp1rp2/2n3pp/pNn1p3/P3P2P/1PPr1N2/5PP1/1R2R1K1 b - - 0 26

Because if you dont, white can get you into trouble by playing h5 themselves on the next move.

White wants to play h4-h5 to weaken black’s pawn structure somehow. Probably not a big deal at 1300 level though.

Thank you. I've just realized now that what I failed to see is the possibility of Nh4-Nf5 later by white. It's like silently reducing black defender pawns (weakening) before the knight goes to occupy squares later.

From the weaker players perspective ...h5 is hard to realize early. For example they could just say if h5 ever played by white I could just ignore it and not letting my king be vurnarable by gxf5. But then they realize the Nh4 by white

1300-1400 level players play h4-h5 as white. Because it's easy to see the future prospect by white. The circumstance is harder for them who play as black because the move is not directly threating the king

If white plays h5 the next move sure you have to take doubling a pawn but I think just not playing h5 is better because it prevents a free Outpost for the knight. Don't listen to stockfish this time!

Or if they play h5 just play g5 now the knight has no decent moves

G6-g5? is exactly what white is hoping for because the white knight becomes a monster after Nf3-h2-f1-g3-f5.

Ng5 is kind of meaningless after f6.

#8 is interesting, but I feel that even if White goes for this really long maneuver, Black will try to stack the rooks along the lines (Red7), and Ne7 can be played at any point. This is also handy because it allows Black to kick the White knight with c6. I’m not saying that g5 is a good move—I just don’t think the knight can be a “monster” on that square. I’m just writing this out of curiosity to see if there’s anything I missed.