Going after the knight would certainly have brought forward White's insurance claim: 21...Qb8 22.Qd2 and the Black Knight's life would have been forfeit for that of his White counterpart.

The threat upon the h-pawn is very much secondary. 22.Rfd1 would have been equally strong.

When one side has all three major pieces lined up on a central file, and the other not even close, you have a pretty fair idea who is having the most fun.

Black was right to apprehend Bb1-a2, but there's the small matter of Rd6-d8 also to consider. Nevertheless, it seems likely that Black ought at once to take the knight, though White gets a strong attack even so: 24...Rxa7 25.Ng5 Ra8 (the threat 26.Rd8 has to be dealt with at once) 26.R1d3 f6 (There's nothing else to be done against Re3-h3, but now Bb1-a2ch is in the air) 27.Rd7! ... whereat 'etc' seems a poor description for the coming dismemberment of Black's position.

A 'tin-opening' move. Black king side is to be opened up like a can of beans.

Retaking with knight makes no difference.