Just an update on this in case it helps anyone else:
- My post on the Boox messageboard got stuck because I put a link in it. It posted after I deleted and tried again without any links. No reply, nor do I expect one.
- My friend provided me with their invoice number from when they bought the Note Pro so I could contact Boox support directly. Boox says firmware 3.2 is not available for Android 9, even after I provided a link from 2 years ago of them, on their messageboard, saying it was in the process of going out to Note Pro Android 9 devices.
- Boox says if you want firmware 3.3.2, then downgrade to Android 6. They provided me with instructions and a link to the required files.
So if anyone wants to upgrade their Note Pro to Android 9, be aware that firmware 3.1 is officially the end of the road.