Moving book notes from Note Pro Android 9 to Note Pro Android 6

[Markismus]

As a happy owner of a Note 5 (firmware 3.5.4) I can sync both my separate notes and my book notes. However, about 2 years of notes in books are still held hostage in my Note Pro with Android 9, firmware 3.2.3. It hasn't got an upgrade to the firmware 3.x that introduced the syncing of booknotes.
To make things worse, the screen is thoroughly trashed, pen input only and it glitches after I repaired the flex cable of the screen under a stereo-microscope by soldering 0.1mm wide connections. My favorite access is scrcpy. That allows me to see it on the PC and interact with the pointer.

Last week I bought a Note Pro with Android 6 with firmware 3.0. So I would like to transfer all data to this one and upgrade the firmware and sync the book notes.

Preliminary questions:

• What files have the book note data?
• Are these files accessible from the internal storage or will I have to root both Note Pro's?
• Has anyone done this before?

Thanks for reading this post! Hope someone can point me in the right direction.