Unfortunately, it is not possible.
The synchronization feature allows you to save your notes in your dedicated cloud service provider: Dropbox, GDrive or iCloud.
All cloud service providers work differently and whereas you can display a list of your notebooks in Dropbox, you can't do it in GDrive or iCloud.
Note that synchronization allows you to save a backup version of your notes, for safety and in case you use multiple devices. Your notes are saved as *.nebo files, a Nebo-specific format. They are not meant to be browsed or opened outside of Nebo, because at this stage, they would not be usable.