OK. I just coaxed the tablet into landscape and fullscreen mode and it’s there. For some reason, Roon doesn’t want to re-draw when the device is rotated. On the tablet, if you start Roon with the device in portrait orientation, there’s no alpha nav element. If you start Roon in landscape (on this particular tablet anyway) it complains about screen resolution and offers “maximized” or “fullscreen”. "Maximized doesn’t appear to do anything but start the app. “Fullscreen”, as it turns out, starts the app a la Kindle, with the notification bar hidden and the alpha nav element is there.
Now. I did that once. Now I can’t get Roon into fullscreen mode , or to run in landscape at all. Even with the tablet locked on landscape, Roon starts in portrait. And with no alpha nav.