@Graphics and Games Engineer I filed feedback as FB12474494.

For anyone who comes across this later, my question was answered by an Apple engineer on the WWDC 2023 Slack: "Quick Look extensions are currently not available on visionOS. I recommend filing feedback with your example to https://feedbackassistant.apple.com/." I filed feedback as FB12290337.

@eskimo, would you be able to help with this? The issue still occurs on iOS 15.1 (19B74).

I'm seeing the same thing. I think this is because UISlider is partially transparent even when enabled.