If you add enchantments to an Enchanted Book so that they fall under the `Enchantments` NBT tag instead of the usual `StoredEnchantments` NBT tag, those enchantments will not reward any XP from the grindstone, but will be removed.

This isn't consistent with all other items, even ones that can't be enchanted in survival vanilla.

/give @s enchanted_book{Enchantments:[{id:"fortune",lvl:3}]}

will give you such a book.

To see the inconsistency, use

/give @s oak_log{Enchantments:[{id:"fortune",lvl:3}]}

Clear your xp, and put both items into the grindstone. Both the book and the log will have the enchantments removed, but only the log will give you any xp reward.