Daniel Yount, a developer discovered an experimental feature called PiP, or picture in picture on the YouTube App. During that time, the feature only appeared on a live stream and not on other playback options.

PiP is available on the iPad, but it’s the first time YouTube is implementing it. Conversely, iOS 14 is set to have this feature when it rolls out this fall.
Steve Troughton-Smith, a developer surmises that the feature could be a result of collaborative work between Apple and Google to bring the VP9 codec to iOS 14 and tvOS 14 and unlock 4K resolution.
Currently, background videos are only unlocked if the user pays for YouTube Premium. The subscription costs $11.99 or $15.99 when you purchase it on iOS. iOS 14 users can get the picture in picture option when they view YouTube videos on the Safari browser.
PiP for iOS is still largely experimental, and it’s unclear whether it will make it on the final version.