white has slight advantage at best here

21..Rfe8 is a mistake because it allows 22 exd4 and now white's advantage is much larger

the computer is right exd4!, by doing it this way, white hands you a weak e-pawn to attack. He probably thought he'd be able to exchange knights on c6.

I would suggest 22. Qg4, threatening mate in g7, but it happens that after Re7, surprisingly, white can't hold the N if he plays exd4 after Ra8-e8, Re2, Bf8, Ra-e1, Nd8!, and white misses a tempo to play Kh1 in order to be able to play d5, saving the N.

Defending b2 preventively, and preparing to add to e3.

White's doing the most of his weak position, but this still keeps hopes in attack. Nf1 would have been pure defence. This move has a downside, yet...

2nd best, this allows 25 Nf5 and white's advantage grows again

White didn't fear this, based on...

simplistic move here. White's timing is off. Nf5 or Qh5 and he is still in business

...probably not exactly this, as suggested!  

It is a mistake because it allows 26 Rf1 and the threat of Nf6+ is very strong.

Thank you kennet! Probably, black's best would have been Rf8,controlling f6 and f5.

the computer analysis is right that white is winning, the comment about the N at the very end is wrong

The pc analysis is a proper tactic melee I would last decades to unravel, and probably wrongly...   -- Charles, of course, now white is a move from mate, since Qxg7# will be unavoidable.

Nf2 is best, white is thinking about defense more than attack here.

Pitifully, the Ng4xh6 strike fails due to the only, superclever defence Qg6, after which white does not have much!

This goes into the computer line, more or less. White's Qc7 is easily answered by Ba8, after which white can play Qc5 or Rf1, trying not to take the Nor Rxc5 will press c3 in addition to e3.

you finally got here. the computer wanted you here a few moves back.

The game is far from the end! Very, very interesting!

whites misses still another chance, either Rd2 or Rd1!

Rd2, h5 and black would win e3, but Rd1 surely helped white's cause.

The c pawn can't advance, this is a weakness white's N are far from protect.