A positional + tactical chess puzzle

White to play and gain advantage.

I don’t understand this puzzle ;-;

Good puzzle . I feel Stockfish when I've found the solution

This is not a tactical puzzle where you win by checkmate or material advantage. Here is f5! the only move that gains the advantage by opening up the centre while black is still undeveloped and king is in the centre. Rest of the moves causes the game to remain around equal as the centre remain closed so black king chilling. However you have to be very accurate and precise to maintain this advantage as this position is very sharp. In fact, Bobby Fischer, right after Bxf5, Re7!, Bxc8? lost the advantage and even later lost the game