An anonymous reader quotes a report from MacRumors:
Apple in iOS 14 added Picture in Picture to the iPhone, a feature designed to let you watch a video in a small screen on your device while you continue to do other things on the phone. The YouTube app doesn’t support Picture in Picture, but up until yesterday there was a functional workaround that allowed videos from YouTube.com to be watched in Safari in Picture in Picture mode. As of today, that workaround is gone, and it’s not clear if it’s a bug or a deliberate removal. Attempting to use Picture in Picture on a video on the mobile YouTube website simply doesn’t work. Tapping the Picture in Picture button when in full screen mode pops the video out for a second, but it immediately pops back into the website, so it can’t be used as a Picture in Picture window. […] Picture in Picture appears to work on the mobile YouTube website in Safari for those who are YouTube Premium subscribers, which suggests that the restriction is intentional and not a bug.