For the new Mac app, we have decided not to offer a free upgrade for existing GoodNotes 4 for Mac customers as we did with our iOS app.
To make the Mac app compatible with the iOS/iPadOS version of GoodNotes, we had to rewrite it in a way that made it impossible to just update the old version of GoodNotes 4. We made that decision because we want to update and support the app for a very long-time and continuously add new, exciting, features to it. We want to invest in the Mac companion app because we believe that having access to your GoodNotes data across devices helps you to make you more productive.
The system we used to provide a free update for GoodNotes 4 users to GoodNotes 5 on iOS, was never intended for this purpose. It is a "loophole" on the App Store and is far from ideal, even though it worked to provide a free upgrade for a lot of our users.
Grey areas and abuse of the system, as well as very bad user experience on the App Store for it, resulting in a massive amount of work for our team, financial damage to our company, as well as in tons of non-self-inflicted bad ratings on the App Store .
We don't regret offering this fair way to upgrade for existing customers of our iOS app and are very thankful for all the support and kind words we received. However, for our Mac app, we have decided to avoid all these problems for us and our customers and follow a very clear and simple pricing strategy: A one-time payment without any hidden costs, subscriptions, or in-app purchases for a premium app that is far better in comparison to its predecessor.
We won't start the argument that "it is just the price of two cups of coffee" because we understand that it is not about the payment itself but about trust: We know that you don't want to pay for every new version that we're releasing.
This is exactly the reason why we have decided to rewrite GoodNotes 5 from scratch. It allows us to update the same app version for a long time and continuously improve it with new features that help you to be more productive. 
We're proud of our work on GoodNotes 5 for Mac and are excited for you to try it out if you decide to still pay the 7.99 USD (or the equivalent in your local currency).
To customers that have bought the GoodNotes 4 Mac app shortly before we introduced GoodNotes 5:
We want to specifically excuse ourselves for the frustration this decision might have caused you. GoodNotes 4 for iOS and GoodNotes 4 for Mac will continue to work on your devices, so you can still use the software you paid for.
 We had many cases were people didn't follow the exact instructions that we provided but instead purchased the app for the full price even though they were eligible for a free upgrade. In other cases, customers ignored the alert that the app wasn't supported on their device's operating system.
 In the future, we may introduce some new features that require additional purchases but they will be optional.