1. Sign in to the same Apple ID.
2. Open the Settings app on your iOS or iPadOS devices, go to Apple ID then iCloud, and make sure both iCloud Drive and GoodNotes are enabled.
3. Open System Preferences on your Mac, go to iCloud, enable iCloud Drive. Click on Options... next to iCloud Drive and also enable GoodNotes in the list.
4. Open GoodNotes, tap the Gear icon in the top-right corner of the Library view then Settings then iCloud Settings, and enable Use iCloud.