Rook and bishop vs. opposite color bishop I drew a game with rook and bishop vs an opposite color bishop due to the 50-move rule.
[FEN &quot;4b3/k1B5/8/2K5/8/8/R7/8 w - - 0 1&quot;]

Is this a theoretical draw? If not, what is the technique to win?
Definitely not a theoretical draw, this should be easily winning for White. The strategy to win would be:


Advance with your king and rook to push back Black's king. If Black's light-squared bishop blocks your rook's check, then this means the Black king is on a dark square. Thus, you can use your dark-squared bishop to check the king and push it back.
Eventually you'll have pushed Black's king to either a light-squared or dark-squared corner.


If it's in a light-squared corner like a8, the light-squared bishop isn't able to act as a blockader from your rook. In the diagram you posted, here's one example of how to win:  1...Kb7 2.Bb6 Bh5 3.Ra7+ Kb8 4.Kd6 Bf3 5.Rc7 Bg2 6.Ba7+ Ka8 7.Kc5 Bf3 8.Kb6. Now all you need to do is maneuver your rook to the 8th rank to checkmate, which can be accomplished in as little as 2 moves.
If it's in a dark-squared corner like h8: Put your king on h6 and move your rook to the 8th rank, checking the Black king. If Black manages to block the check with ...Bg8, then you can checkmate immediately by moving your bishop onto the a1-h8 diagonal.