Hi Hans!
Re: "How can I find a list of all the books in the Books app?"
Seems the "Library" in the Books App contains all the books, whereas the various "Categories" sort the books into sections to make them more manageable.
Apple support's online aticle: Read books in the Books app on iPad - Apple Support
Eg: says:
"Library: Tap to view all of the books, audiobooks, samples, series, and PDFs you either got from the Book Store or manually added to Books.
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Re: "I like to list all the books which are imported from my Mac mini, until now,
but can't find such a list with Finder. Is there any at all?"
Also: Seems you can change the display to view as a list:
Organize books in the Books app on iPad - Apple Support
Eg: says you can:
"Organize your books
You can change how the books in your library or a collection are displayed and sorted.
- Go to the Books app
on your iPad. - Tap Library or go to a collection.
- Tap
, then do either of the following:
- Change the book display: Tap Grid or List.
- Change the book order: Tap Recent, Title, Author, or Manual.
- If you choose Manual, touch and hold a book cover, then drag it to a new position."
You may want to create a collection to contain all books you have imported from Mac Mini.