I don't understand white's move 43.Qf2 abandoning the bishop to his fate, is it forced somehow?
I didn't either. Perhaps, he was frustrating defending all the time. The position was nearly zugzwang :
if his bishop moved, then 43... Rc2. As for the queen move, he has only two options so he could defend his bishop : either 43. Qb2 or Qc1. I would then respond with 43... Qd3 and he would lose his bishop.
The best move in that situation, as also recommended by Stockfish is : 43. a4. This pawn move at least would have help him stand longer.
When this Rapid 15|10 min game appeared, I didn't expect to face a 2000s opponent. Into this game, my opponent's rating was 2010, mine was 1691. But then I said to myself : "Ok, I am ready". While feeling nervous at certain moments, I felt quite confident.
In the midgame, I found chance to trouble him with my knight maneuver that eventually gave me an advantage. I tried my best to maintain this advantage. It still required patience and accuracy, though, to do a breakthrough, as he defended well. Eventually, I found a breakthrough move : 36. b4 (Stokfish considers it the best too). With this pawn sacrifice, my rooks could enter opponent's territory from c file. Eventually, he resigned.
I have beaten two 2000s rated players previously, but those wins are questionable. One opponent resigned without obvious reason, while the other left his clock run without making move on his turn in a Rooks + Pawns endgame, until he got flagged. Now, this time I win convincingly.