Castling can be abit confusing, like En Passant. However, remember that Castling may be done only if the king has never moved, the rook involved has never moved, the squares between the king and the rook involved are unoccupied, the king is not in check, and the king does not cross over or end on a square attacked by an enemy piece. In this game the King never crossed over or landed on the attacked b8 square, only the rook did. Don’t worry, even Grandmasters can be confused over castling rules, like Legendary Victor Korchnoi who during a Candidates match with Anatoly Karpov in 1974 went up to the arbiter and confirmed he could castle while his rook was under attack. He isn’t along either, check here for other Chess masters who made mistakes about the rules! https://www.chess.com/amp/article/do-grandmasters-know-the-rules-of-chess
Hope this helps clarify the matter and make you feel at ease for being confused about it to!
In this game
, why is move 20 O-O-O possible... I thought the bishop spanning the diagonal f4-b8 would prevent that? Was surprised when the opponent played the move, as I (in part) placed the bishop there to prevent that
Thank you for the help!
https://www.chess.com/analysis/game/live/3839788312