Why we are removing iPadOS 13 support:
Maintaining support for iPadOS 13 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 14.5 or later. If your device software can't be updated from iPadOS 13, 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 13
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 13 and newer iPadOS may cause sync issues).
Note: The oldest version of iOS that GoodNotes 5 works on is iOS 14.5. As such, if you're currently on iOS 12 or earlier, you would also be able to continue using GoodNotes 5 on your existing update (without access to some functionality).