1. You can create an app via SwiftUI. Apple has a sample just for this

Choose Your Own Story Provide dynamic navigation between views. In this sample, you can write a story with many different paths and outcomes. Your reader can make choices at important points in the narrative, resulting in different experiences based on their responses. There are several parts to this app. StoryData contains the story itself, including the text on each page and the choices the reader can make. StoryView sets up the navigation for the app, and StoryPageView displays the contents of one page of the story. You can start in StoryData and write your own narrative, or you can learn about and modify the look and feel of the app in StoryView and StoryPageView.

2. I'm unaware of the possibility of an Interactive book for Apple Books. There is probably a way to use links for the pages, but I have not seen anything like this before.