i agree with you that in the final position it should be the easiest way to win for black to exchange the f2 pawn to the h2 pawn and get two connected passers.

But i think 54...g3 wins too. I have only the look on the screen, no board, no chessprogram available, so i may be wrong, but i see:

55.hxg Kxg3 and then bring the black bishop to g3 via f6, h4 to protect both pawns and get the king free for moving around.

Black has two ideas:

First, to exchange the h pawn to b5 pawn, if the bishop protects the long diagonal, and reach a won ending

Second to bring the king to e1 (e2) if the white king moves to g2 and the bishop protects f1-b5

Carlsen was steadily improving his position and advantage but Brynell blundered on 46 with Be8??. Keeping the bishop on the h1-a8 diagonal was critical at that point. After 46.Be8 the eval skyrockets from 3.00 to 9.79

Then at 49...e2+ is the correct finish with the eval at 17.74 but after Qxe1+ it goes all the way down to 3.84