we have run into the same problem and found it is related to presence of the VRAPP flag in the app manifest. This also seems to control if launcher/libraries display the app entry at all, so we had to use two apps and let them call into each other.
However - since a recent device OS updated on our Focus3 this does not seem to work any longer and the Webview is now always rendered as you describe, even if the flag is not set.
@cboulanger: Did you maybe manage to solve this - or is there maybe an alternative / recommended way?
Webview support
in VIVE Focus 3
Posted
Hey Jan, did you find a solution to the problem?