Lecturing on this game, Yusupov makes it clear that the deepest move (I would say, the elite GM move) in the game is in this position:

Black to play

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What does white want to do? There are three plans:

a) Charge in the center with c4 and d5
b) Nxf7 may one day be a serious threat
c) Qd3 and Bc2

He looks for the move that prepares black against all three, and finds it.

19...Rc7! Now:

a) If white plays for c4-d5, black has options, like Qc8, Rd8. b) The strength of tactics involving the knight sac diminishes considerably now that black has a rook on the seventh rank. c) If white plays for Qd3 and Bc2, black plays as in the game.

At this point, black has a comfortable game.

When Yusupov played 24...g6, he says that Gavrikov should have prioritized prophylaxis with 25.Qe3, which stops Kg7. Instead, he chose to improve his position with 25.Re1. Yusupov notes that <prophylactic thinking often trumps our standard concern with improving our position> because it takes more seriously what our opponent is trying to do.

White's decisive mistake is 28.Qf4. He had to play 28.Nxf6 Qxf6 29.Re5 and enter a rather unpleasant endgame where he needs to fight for the draw. (Yusupov says the draw should be possible with accurate play. He also says he did not think of this line as the best option for white during the game.)

After 28.Qf4, Yusupov asks us to think what black should play.

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Now is the time for black to improve his position... decisively! The stage is set for the DSB bishop to transfer to the dangerous h2-b8 diagonal, and all of black pieces are poised for the attack.

28...Be7!

And Yusupov says that black is winning. The computer agrees and evaluates the position as -2.3. The computer assesses 28.Nxf6 (instead of 28.Qf4) as even (-0.12) but of course, as we all know, the computer does not consider a position more or less <difficult to play> for a human.