I created a new Spatial Rendering App from the template in Xcode 26.0.1. When I run the app, click 'Show Immersive Space' and select my Vision Pro from the pop-up dialog, the content in the dialog flickers (which seems to indicate something crashed) and nothing appears on my Vision Pro.
I'm running the released macOS 26.0 (25A354) and visionOS 26.0 (23M336). Filed as FB20397093.