The official Adobe page explaining about the navigation of the XD mobile app doesn't mirror at all what I see or experience on my Samsung S7+. There's no way of navigating as described at all. I can swipe between artboards and that's pretty much it, but I have no navigational buttons to take me back to the index of CC or anything. With InVision I can navigate back to all my artboards, back to the first page of the artboards from my document, out of the whole app and back to the index etc. With XD mobile all I can do is swipe between artboards within a document but other than that I'm totally lost.
Well, the app doesn't have any navigation menu other than some function buttons on the very firsts page, it lacks ways to navigate trough the projects and get an overwiev of the projects other than what you see on the very first page. There's no finger gestures that replaces navbuttons either. So there's no navigation really. That's what I meant. I have posted my opponion about that in the feedback but one should think Adobe didn't need people to tell you that it's not possible to navigate in the XD mobile app.