How can white win after 55. BF2?

I agree, there is no way to break the blockade without losing the game. And mating with the Queen alone won't happen. Computer won't admit it for some reason which is , I assume, why you posted your game here. Dead Draw.

I beg to differ, there is a win, you can force a zugzwang.
1. You put a queen.
2. You grab the g6 pawn.
3. Next we assume that the bishop stays on f2 and doesn't move, because if it moves it's lost, there's always a way to fork it after a series of checks. Or at the very least, if it hides on g1, the g3 pawn falls.
4. You use the queen to force black king into a corner until it's "stalemated". Black then has to move the bishop. Then the bishop or the g3 pawn is lost.
I haven't tried it against an engine but seems pretty solid to me.

@JiaruiLiu
Nice! Even though Stockfish will claim a win for white I don't see how white can proceed. 1/2 - 1/2

The "100 endgames you must know" book has a chapter with lots of draw fortresses, pretty cool.

@huellyouhappy What if the bishop moves to e1 then?

@JiaruiLiu Then, as I said, you start checking the king, aiming to fork the king and the bishop. Once you start checking, the bishop won't move anymore, so you'll always be able to force a fork.

@huellyouhappy
The bishop will stay on f2. What is your winning plan for white ? What do you mean with fork ?
The white king position is so bad.

Actually, tablebases claim a win for white :( Zugzwang is indeed possible !

lichess.org/editor/8/8/6Q1/8/8/6p1/3k1bPp/7K_b_-_-_0_1

@huellyouhappy How can you “stalemate” the king(if the king moves close to the bishop)?

@JiaruiLiu You have a queen, the queen is always able to force king into stalemate without any help. The bishop is on the f-file, the king is on the c-file, the king will never approach the bishop while the queen is between them. Again, if the bishop leaves the f2 spot, you fork either king and bishop or king and g3 pawn. Queen is omnipotent on an empty board.