What is this side bar feature called?

I've gotten a few complaints from some users that are using iPads saying they are unable to interact with certain elements of my app (gestures, taps, touchesbegan/moved don't seem to be working). The issue seems to be spread among the different models but also doesn't happen to all iPads.

When I try debugging on any iPad simulator, I don't seem to have any issues with it. I've asked one of them to send me a video of them interacting with the app and the only difference I can see is this side bar. I haven't encountered this before but can't seem to find the name of this feature to look up how to turn it on so I can see if it's causing any issues.

Does anyone know what this collapsable menu is called? Also, while I'm here, does anyone know why certain interactions don't work on the iPad?

That little tab represents a video playing in system Picture in Picture when the video is stashed off the side of the screen. You should be able to recreate this UI by playing a video in Safari or the TV app and then swiping home to move the video into Picture in Picture.

What is this side bar feature called?
 
 
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