@TeamYouTube had responded to a question about the now ended experimental support for PiP that was available to YouTube Premium users, saying "the Picture-in-Picture feature is still rolling out & will be available in a matter of days across all iOS 15+ devices."
That message has now been deleted and replaced with...
--- Hi again! Previous tweet was about PiP coming to @YouTubeTV – deleted to avoid any confusion!
For YouTube: PiP was temporarily available on http://youtube.com/new for Premium (only until April 8), it's not widely available yet, but working on it, updates to come soon! ---
The mixup is likely to increase frustration among users who have been waiting for the feature since it launched with iPadOS 13.