[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR"] [Title "Berlin Defense"] [StartFlipped "1"] 1. e4 e5 2. Nf3 Nc6 3. Bb5 Nf6 4. O-O Bb4?!
When White castles, Stockfish evaluates the game to be roughly equal. After Black responds with Bb4, the evaluation goes to around
+1 and Stockfish labels it as an inaccuracy.
What is wrong with Black’s move? It leads to a more symmetrical position so I’m surprised that it’s considered bad.