With macOS 10.15 Catalina, native installers such as .pkg or .dmg require to be 'notarized' with Apple. It's less scaring than it sounds, let's see how please the Gatekeeper.
If you're willing to produce digital books to be sold by Apple, be aware that each one of the available tools will shape your content and how it is going to be delivered in a very peculiar way. This post will cover InDesign, iBooksAuthor and the Adobe Digital Publishing Suite targeting Apple iBookStore and AppStore with ePub, iBooks and Apps. Which one does fit your needs the best?