That specific moment is actually pretty basic. You're right that it was a great match to watch though.

In hindsight, yes, it's basic for sure. But in the heat of the moment after 7 hours of thinking about nothing but chess, Ian obviously missed the potential fork and was visibly surprised that Magnus left his rook to be attacked.

He didn't miss it though - if he had, he would have taken the rook. No one at their level misses something like this in these games. This stuff is obvious to much much weaker players than Ian.

Replying to sibling: no, he was not - it was obvious, even to a low-level recreational player (like me)

Copying what I said in another reply: I'm referring to move 133, right after Ian moved his queen from H6 to H7, attacking the rook. Magnus ignores this and moves his E5 pawn to E6. https://www.youtube.com/watch?v=PWkBeTwbfj4&t=29890s

If he was aware of it, he would not have allowed it occur to begin with. He was counting on Magnus to move the rook and was very visibly surprised when Magnus left the rook in place.

You mean Rf7 when he ignored the *pawn on e6 being attacked by the queen for a potential fork with the knight (Qxe6 Ng7+)?

I'm referring to move 133, right after Ian moved his queen from H6 to H7, attacking the rook. Magnus ignores this and moves his E5 pawn to E6. https://www.youtube.com/watch?v=PWkBeTwbfj4&t=29890s

The match was already lost at that point. Two moves before that, Stockfish 14 has mate in 49.

Stockfish having mate in 39 moves says nothing about a match between 2 humans, already having played for over 6 hours, under very limited time constraints.

Did Stockfish have a mate at 131. Kh4 Qe6+?

Yes. You can check it out here - http://analysis.sesse.net/ - just click on history. (Sesse is Stockfish with a lot of compute, you can also follow it live during the games). At 131 it says "White mates in 47".