I've had several PDF books/articles catalogued in Books, and now they are all completely gone (all but 1!) in Big Sur.
I use iCloud, and they were synced there as well, as I could see these same files on my phone or iPad.
Is this expected behavior? Where have my files gone?
thanks,
Alex
For some time. I could not fix the issue and found the solution today. Go to System Settings -> Apple Id -> iCloud ->
iCloud Drive -> Apps Syncing to iCloud Drive -> Switch on BooksApps Using iCloud -> Show All -> Switch on BooksFor sure you need to be logged-in with your apple id in the Books app etc.