I have a similar issue. Did you ever find a solution to your issue?

I need to use Designed for iPad until certain third-party frameworks are updated to support visionOS. I would like to make the background of the app semi-transparent (low alpha) to reveal the surroundings behind the app. The best I can get is a black background, even with a clear window and view. Is there a way to make whatever is behind the window (the UIScreen?) clear as well?

+1 as of 10 minutes ago.

Rebooting worked for me.

It's back. Same errors. Tried all the previous fixes - no joy.