It appears it can only be done on certain apps using picture in picture. From the User Guide.
“Multitask with Picture in Picture on iPad
With Picture in Picture, you can use FaceTime or watch a video while you use other apps.
When using FaceTime or watching a video, tap or press the Home button (models with the Home button).
The video window scales down to a corner of your display so you can see the Home screen and open other apps. With the video window showing, you can do any of the following:
Resize the video window: To make the small video window larger, pinch open. To shrink it again, pinch closed.
Show and hide controls: Tap the video window.
Move the video window: Drag it to a different corner of the screen.
Hide the video window: Drag it off the left or right edge of the screen.
Close the video window: Tap .
Return to a full FaceTime or video screen: Tap in the small video window.”
Excerpt From
iPad User Guide for iPadOS 13.1
Apple Inc.
https://books.apple.com/us/book/ipad-user-guide-for-ipados-13-1/id1464778568
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