@albert its correct / expected that Video Preview is grayed out if you have the device assigned to some app
when you unassign/uninstall the app - the "Video Preview" becomes available
that you see no preview stream yet & identifying means that the "default" application that runs in the background is likely still downloading/installing - not running - and as such device wasn't identified
you don't need to wait for this to finish - simply install some app you want and the video is then under Live View tab of said app