I have been analyzing this endgame for a while now, but I can't seem to make any progress. The engine evaluation is -2.5, but I'm wondering if this is one of those weird evaluations that is wrong because black can never win.
Black to move
8/8/8/1q4p1/p6k/B1R4P/K7/8 b - - 0 1
It does look like a fortress. After 1...Qe2+ 2.Bb2 Qd2 White can wait with Ka2-b1-a2 or Bb2-a1-b2 depending on where the queen sits.
Black cannot bring the king to d4 because of discovered checks, so the best try seems to be to travel to d5 and play a3 when the pieces are Qd2, Bb2, wKb1. Then Rxa3 Kc4 prevents the rook from coming back to c3 because of Qxc3 simplifying to a winning pawn ending.
Alas, White still can play Bc1 Qg2 Re3 Kb4 Ra3 and wait with Ra3-e3-a3.
I believe it is a draw.
It would be perpetual since white can keep the rook on the 3rd file and guard it with the bishop, your best bet is to hope they blunder, which isn’t likely
I checked the tablebases, and removing the a3 pawn is a win for black, while removing the a3 and b5 pawns is a draw.
I ran it through a couple of engines for a while, starting with Qd5+, Kb2, Qd2+. It did not appear to come up with anything.
