When you rename the advancement book with a player name and use it, it should attempt to load all the advancements of that player (if they have logged into this world before). It should also display the name of the player at the top of the GUI somewhere.

This would give more function to the advancement book, and it's nice to see how your game partner is progressing.

This mod does not add a book, and doing something like that is also not really in scope of what I want to do with this mod.

Happy to work with the owners of the advancement book mod, if I need to leave some hooks for them to get this working with my mod.

Oh sorry, I must have messed up finding the right mod for the book.