I've laid out a book in InDesign (CC v 16.4) on a Mac (Montery v 12.1). The entire book is in one document but each chapter is a separate story. When I export to reflowable ePub, I can't get the chapters to start on a new page. They all flow from the chapter before with just the space I've assigned in the "chapter #" paragraph style I created. How do I get the chapter to start on a new page?
That's pretty much how it's done in all documents, print, PDF etc.
With EPUB, though, it depends on the reader. Not all of them will break to a new screen-page on a page-break directive, because of the HTML basis for the document. It works on through to Kindle and in some small-screen readers, but if you open your doc on a full-screen reader like a browser plug-in, you won't see page breaks.
|| Word & InDesign to Kindle (& EPUB): a Professional Guide (Amazon)