About EPUBs created with iBooks Author
iBooks Author 2.3 and later includes EPUB templates with which you can create media-rich books compatible with Apple Books and other EPUB readers.
Here's what the iBooks Author EPUB templates can do:
Export to EPUB 3 format.
Allow the reader to read in both paginated and scrolling view.
Allow the reader to change the font size in the book.
Can include some interactive widgets, such as movies, audio clips, HTML, and image galleries.
Can be viewed in any EPUB reader that supports EPUB 3.
When you view EPUBs created with these templates in Apple Books, they'll look like they did in iBooks Author. In other reading applications, they might appear slightly different. Also, you won't be able to change fonts or view EPUBs created with these templates in night mode.