documentation ?

No, there is not.

Since version 7.0, the shortcode [pgn] ... [/pgn] remains supported only because of legacy content. It is now advised to use the Chess diagram / Chess game blocks, as presented in https://rpb-chessboard.yo35.org/. In particular, with the blocks, all the customization options are made available graphically (in the right-side column of the block, see https://rpb-chessboard.yo35.org/examples/navigation-board/ for an example). This is much less cryptic than the navigation_board=below syntax available with the shortcode.

Please use the GitHub as much as possible instead of this forum for help requests, bug reports and feature requests:
https://github.com/yo35/rpb-chessboard/issues