The black player was rated 2436???

That's a FIDE International Master-level rating. And yet he played nearly like an amateur for many moves.

First, between moves 8 and 12 he spends five entire moves in the opening rearranging his knights in dervish dance for no apparent purpose, while leaving his queenside bishop and rook undeveloped -- where they remained, useless, until the end of the game.

Then for the next three moves, he moves his queen around in a tight little circle as well, again with no apparent goal in mind, while continuing to leave his other queenside pieces undeveloped.

Then between moves 18 and 20 he once again moves his queen in circles for three moves -- now that's six moves in total futzing around with the queen -- with no strategic goal in mind.

And then on moves 28 he walks face-first into a mate in two -- which his opponent didn't even need to see, because there were other ways to beat him as well.

OK, I could imagine a little kid playing against Carlsen this way in a simul. Or maybe a 1300 player.

The way I finally solved it was with rigor.

1. White had nothing going except the possibility of mate.

2. Mate was very unlikely unless White could cover f7.

3. f7 was very hard to cover unless Black's knight moved -- and that has to be "moved" rather than "captured".

4. Qxg6+ was the only way I saw to force the knight to move ...

Black's decisive mistake appears to be 22...cxd4?, allowing 23. cxd4 +- (+2.61 @ 21 ply, Stockfish 9). Instead, 22...Nc4 23. Bc1 e5 24. dxe5 ± (+0.89 @ 19 ply, Stockfish 9) keeps Black's survival chances alive.

A wee bit harsh on the lad.

You can see a logical reason behind all of Black moves including 28...Kf6 are not random moves and just made for fun. (also we must remember it was a rapid game. 15 + 2 secs for the game)

here: Black to play.

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Black is lost no matter what he plays.

28...Kf6 breaks the pin and holds the g6 pawn.

Make no mistake. Carlsen will be disappointed with himself for missing the classy mate. I know I would.

28...Kf6 29.e5+ dxe5 30.Qxg6+ Nxg6 31.Nh5+ Kf5 and mate with a pawn. 32.g4 is also pretty.

The play with the Knights was OK. and the Queen to b6 was to hold up d4 and dissuade a 0-0-0 and the move g4 which is the usual follow up to early h4's. At this speed you are guided by general ideas both for and against you.

Then the Queen poked about on the Queenside hitting d3, preventing b4 and trying to hold back d4.

The bad move IMO (remembering this was a rapid game) was here:

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White has got in d4 and Black in typical Sicilian Mode played 22...cxd4 (probably automatically) and the open c-file did him. 22...Nc4 was better.

That is hindsight analysis. But anything that allows a Rook a free trip to the 7th must viewed with suspicion.