I just purchased a used 2019 F350. My back up cam works fine. I also have he other cam on the tailgate just off to the side of the handle. And I have the center high mount bed cam. However I cannot find how to switch between these. In reverse I only have the zoom button on the screen. If I push the camera button above the display, I get a black screen and no cam detected. I figured if it has the cameras, surely they are setup.

 

The one just to the side of the tailgate handle is a light, not a camera.
If the camera in the CHMSL isn't showing when you tap the button above the screen, then you have a camera or harness issue.
You might check for a recall or notice for the camera.