I really like your WinBoard program. I use Winboard 4.2.7 and Winboard 4.8.0 to watch games by downloading and opening the archive in pgn format. On the website
https://tcec-chess.com/#x=archive there is an archive of computer engine games, for example, Season 21, where FRC 4 is Fischer Chess 960: Winboard 4.2.7 Winboard 4.8.0 does not show Fischer chess 960 games, they write an error message "Illegal move" on moves 0-0; 0-0-0 and other moves if there are comments in parentheses in the pgn text. In previous seasons, computer engines also played Fischer's 960 chess, and Winboard also writes an error message "Illegal move" on moves 0-0; 0-0-0. Please fix these Winboard errors to be able to view Fischer's 960 chess games.