Problems to sync iPhone via Finder

Perhaps the User overlooked some information from one of the links supplied earlier.

Just incase - here is a Copy and Paste

See your books and audiobooks on all your devices with Books on Mac - Apple Support (CA)

See your books and audiobooks on all your devices with Books on Mac

With iCloud, your books, audiobooks, PDFs, collections, highlights, notes, and bookmarks appear automatically in Books on your Mac, iPhone, iPad, and iPod touch when you’re signed in with the same Apple ID. If you purchased a book or audiobook on another device, you can easily download it on your Mac.

With Bluetooth, your audiobooks appear automatically in the Audiobook app on your Apple Watch and CarPlay, so you can listen on the go.

See books, audiobooks, and PDFs you added to Books

• On your Mac: Choose Apple menu  > System Settings, then click [your name] at the top of the sidebar (if you don’t see your name, click Sign in to your Mac to enter your Apple ID or to create one). On the right click iCloud, click Options next to iCloud Drive (make sure it’s turned on), then select Books.
• On your iPhone, iPad, or iPod touch: Go to Settings > [your name] > iCloud (or Settings > iCloud), turn on iCloud Drive, then scroll down and turn on Books.

See books you’re currently reading, collections, bookmarks, and more

1. In the Books app  on your Mac, choose Books > Settings, then click General.
2. Do any of the following:

• • Select Reading Now to see what books and audiobooks you’re reading across your Apple devices.
  • Select “Collections, bookmarks, and highlights” to see your collections, bookmarks, highlights, and recent book info across your Apple devices.

Listen to audiobooks on the go

• On your Apple Watch: By default, up to two audiobooks from your Reading Now or Want to Read collection sync to your Apple Watch. You can also sync audiobooks to your Apple Watch manually. See Add audiobooks to Apple Watch in the Apple Watch User Guide.
• With CarPlay: You can listen to audiobooks while you drive. See Play audiobooks with CarPlay in the iPhone User Guide.

Manually update and transfer items between devices

You can also use a cable to update and transfer items between your Mac and an iPhone, iPad, or iPod touch. See Intro to syncing your Mac and your devices.

You can hide books and audiobooks you purchased from the Book Store that you don’t want to see on your devices. Hidden items don’t appear in your library or in iCloud. If you have Family Sharing set up, your family members can’t see or download hidden books or audiobooks.

In the image presented above, we are seeing the General Tab

As per the information fro Apple you need to a different tab like music or such

The Audiobook are collected and placed in the Books Application

Refer to links below on these topics

Use the Finder to sync your iPhone, iPad, or iPod with your computer - Apple Support (CA)

See your books and audiobooks on all your devices with Books on Mac

Work with us here if you would.

The AudioBooks are located on which Device ?

The AudioBook are listened to in what exact application ?

Welcome

The " Devil is in the Details "

What used to work in Older Versions of macOS may still work but in a different may in Newer Versions of macOS