user23297: In the game Isaak Boleslavsky versus Vassily Smyslov of the USSR Championship 1961 the following same colour Bishop endgame was reached. On move 46, the position is WHITE King on b3 Bishop on e3 pawns on b5 d5 e4 f2 g2 h3 BLACK King on e7 Bishop on d8 pawns on d6 e5 f6 g7 h7. BLACK to move.
[FEN "3b4/4k1pp/3p1p2/1P1Pp3/4P3/1K2B2P/5PP1/8 b - - 0 1"]

Soviet commentators hailed this endgame as a Smyslov defensive masterpiece (the game ended with a draw) and Aveskulov agreed. But Stockfish 14.1 NNUE depth =66 seem to indicate White missed a win. Indeed, after several minutes of analysis Stockfish changed its apparently fixed evaluation of +3.60 and evaluation starts to go up. Black than switched to new system of defense, but the evaluation remained then at +4.14. I tried then to follow some moves in the line indicate by Stockfish and did a second iteration some moves forward. It seemed a White win indeed (evaluation at +6.93 at comparable depth).
What happens with perfect play? And why did no commentator pointed to at least a potentially approach for White? In the end, Soviet grandmasters considered this position a fortress, But Stockfish 14.1 NNUE disagrees. Why?

user14079: Partial answer : There is no contradiction
The fact that the game was eventually drawn doesn't mean that this position is drawn with perfet play. The fact that Smylov created a "defensive masterpiece" doesn't mean that Boleslavsky hadn't have mistakes on the way.
Even before computers becamae oracles, I think there was little doubt among grandmasters, including Boleslavsky and Smyslov themselves, that this position should win for White: he has a sound extra passed pawn, more space, the better bishope, and possibilities to create a second weakness on the kingside (most probably by pushing the f- and g-pawns under favourable circumstances, but that's not the only plan).
Yet this is not easy to win. The point of Smyslov great defensive effort was to make it as hard as possible for Boleslavsky to convert, to have him make some tough decisions on the way, where he could go wrong without making any obvious blunder.

A full answer would need to be focus on the actual game continuation, commentators' thoughts about it, and the Stockfish lines that the OP talks about but doesn't show. Once this is added in the question, I will try to find time and improve this answer accordingly.

23297: <p>In the <a href="https://www.365chess.com/game.php?gid=2558025" rel="nofollow noreferrer">game Isaak Boleslavsky versus Vassily Smyslov of the USSR Championship 1961</a> the following same colour Bishop endgame was reached. On move 46, the position is WHITE King on b3 Bishop on e3 pawns on b5 d5 e4 f2 g2 h3 BLACK King on e7 Bishop on d8 pawns on d6 e5 f6 g7 h7. BLACK to move.</p>
<pre><code>[FEN &quot;3b4/4k1pp/3p1p2/1P1Pp3/4P3/1K2B2P/5PP1/8 b - - 0 1&quot;]
</code></pre>
<p>Soviet commentators hailed this endgame as a Smyslov defensive masterpiece (the game ended with a draw) and Aveskulov agreed. But Stockfish 14.1 NNUE depth =66 seem to indicate White missed a win. Indeed, after several minutes of analysis Stockfish changed its apparently fixed evaluation of +3.60 and evaluation starts to go up. Black than switched to new system of defense, but the evaluation remained then at +4.14. I tried then to follow some moves in the line indicate by Stockfish and did a second iteration some moves forward. It seemed a White win indeed (evaluation at +6.93 at comparable depth).</p>
<p>What happens with perfect play? And why did no commentator pointed to at least a potentially approach for White? In the end, Soviet grandmasters considered this position a fortress, But Stockfish 14.1 NNUE disagrees. Why?</p>
 14079: <p>Partial answer : <strong>There is no contradiction</strong></p>
<p>The fact that the game was eventually drawn doesn't mean that this position is drawn with perfet play. The fact that Smylov created a &quot;defensive masterpiece&quot; doesn't mean that Boleslavsky hadn't have mistakes on the way.</p>
<p>Even before computers becamae oracles, I think there was little doubt among grandmasters, including Boleslavsky and Smyslov themselves, that this position should win for White: he has a sound extra passed pawn, more space, the better bishope, and possibilities to create a second weakness on the kingside (most probably by pushing the f- and g-pawns under favourable circumstances, but that's not the only plan).</p>
<p>Yet this is not <em>easy</em> to win. The point of Smyslov great defensive effort was to make it as hard as possible for Boleslavsky to convert, to have him make some tough decisions on the way, where he could go wrong without making any obvious blunder.</p>
<hr />
<p>A <strong>full answer</strong> would need to be focus on the actual game continuation, commentators' thoughts about it, and the Stockfish lines that the OP talks about but doesn't show. Once this is added in the question, I will try to find time and improve this answer accordingly.</p>
