You may be expecting to synchronise your notebooks of GoodNotes 5 on iOS/iPadOS/macOS on other platforms such as Windows or Android. However, there are limited functionality right now since Windows/Android app is still in development.
At this moment, the document library in GoodNotes for Windows/Android do not sync with GoodNotes 5 for iOS/iPadOS/macOS.
However, in order to share your notebook on iOS/iPadOS/macOS, you can generate a share link of your notebook to access it from your browser (available in full version only). If you're also using GoodNotes for Android/Windows, you can now edit that notebook on the non-Apple device or from a browser. Please check out this article on how to share your notes cross platform.
Q: I am using GoodNotes 5 on iPad, Can I login GoodNotes for Windows/Android with the same email address for iCloud and see my documents across devices?
A: No. The accounts for iCloud and GoodNotes for Windows/Android are separate. To share your notes on Windows/Android/Web, you can create a Share Link.
Q: l have registered the same email for Microsoft Account and Google Account, can I see the notebooks synced between GoodNotes for Windows and Android?
A: No. Microsoft account is different from Google Account, even if the email address is the same.
Q: Can I sync my document library across GoodNotes for Windows and Android?
A: Your documents of GoodNotes for Windows/Android/Web are stored in one place, simply login to the same GoodNotes Account to access them.