Hi David,
Thanks for reaching out about this. The option to publish a Storyline file as a video can be a handy way to share your course. Unfortunately, the MP4 video output creates a standard video, not an interactive one. So it's an excellent option for content that can automatically play, but not for content you want learners to navigate through with Next and Back buttons.
If you want your final published course to have interactions like Previous and Next buttons, you'll want to use one of the other publishing options, like Web or LMS/LRS. And while it's not as commonly used these days, the CD publishing option will allow you to create an interactive file that you can distribute to learners as well—whether you share it by a physical device, shared drive, or file sharing service.