Why we are removing iPadOS 12 support
Maintaining support for iPadOS 12 limits our ability to ensure a reliable, high-performance experience and deliver the newest improvements and technology. The latest iPadOS versions provide better capabilities to improve the efficiency with new technologies.
What you can do
Please open the Settings app, tap General > Software Update and see if you can bring your device software up to date to iPadOS 13 or later. If your device software can't be updated from iPadOS 12, we highly recommend upgrading to a newer device to ensure you can get all future updates of the app.
If you choose to stay on iPadOS 12
You'll still be able to use your existing GoodNotes 5 installation as usual, but unfortunately will no longer receive future bug fixes and improvements to the app. For example, iCloud Sync and Auto Backup with third-party cloud services may be affected when we introduce new improvements/bug fixes for those features in the future (i.e. using multiple devices on iPadOS 12 and newer iPadOS may cause sync issues).