Thanks – I gathered as much from the documentation. Reason for asking though was that the Photos app displays the vignetting around the spatial movies, whereas in the Destinations app code, for instance, when docked in an immersive space the videos are displayed in sharp rectangles. Is this just a product-design of the Photos playback experience? (The vignetting?)

Gotcha - thanks again for the reply!

Just FYI – this doesn't resolve with modelsortgroupcomponents. Like, if you're building a tree in the standard way of using cards with transparency to define leaves, etc, you'll end up with sort issues like the OP's, all over the place. And there's no way to define which order these leaves should be in – it would be completely impractical. Note that if you turn on 'opacity threshold' this problem disappears. But this isn't really a solution, as opacity threshold results in horrible aliasing.

Thanks for replying, I posted a new message in this thread with an image showing the setup and the relevant snippet of the UDSA file. Using a preview surface, but still no luck. As you can see, the model just displays its base polygonal hull, rather than a smoothed subdivision surface.

Omg, you rock - thank you. Yep, this works!

Haven't tested it out but in theory it should work just fine programmatically if you assign a physical material and NOT a shader graph material (which is sometimes referred to interchangeably in the docs as MaterialX.)