Can someone please help me analyze this game

Didn't really understand where did I give advantage to opponent, can someone help?

It really started when you gave your opponent the knight outpost on move 19. The knight constricts and paralyzes your position while giving black more play. After allowing the other knight to e4, you're just in a really bad position. Your opponent played well, taking advantage of the queen-side majority to create more opportunities while inhibiting your ability to counterattack or do anything in general. You gave your opponent much more space and much better squares for his/her pieces. Your pieces, as of move 23, were mostly stuck on the 1st or second rank and were staring into pawns. Finally, your blunder on move 26 sealed the deal. Your opponent was completely crushing you, with more material, space, and piece activity. I think on move 18, you shouldn't have pushed the pawn, and instead kept the tension in the center. The knight can't jump in, your pawn is protected, and all is good. Hope you enjoyed my analysis and good luck!

The eval switches to favor black on move 18, when you commit to playing queenside, where black is stronger, instead of playing on kingside, where your strong pieces and the enemy king are. Once your c pawn is pushed, black has two pawns marching down queenside with only one pawn to stop them; you've lost queenside already.

It's compounded by not paying attention to where the enemy knights can go; 19. Nb3 gives black's knight the powerful c4 square, and 20. Qc3 gives the other one e4 with tempo. You don't clear space for your own knight, so it gets pushed all the way into the corner. When your knight comes back out, it's to cut off defense of c3, allowing the queen/rook fork.

So, biggest advice is, learn those knight moves. They're called "tricky knights" for a reason, and you've gotta learn the tricks.