How to display custom UI in Picture-in-Picture after iOS 15

After Picture-in-Picture is opened on the camera interface, the custom UI cannot be displayed. Is there any way to make the custom UI visible? If custom UI cannot be displayed, how do teleprompter-type apps in the store manage to show custom teleprompter text within the camera?

How to display custom UI in Picture-in-Picture after iOS 15
 
 
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