Picture-in-picture (PiP) mode was one of the newest iOS features introduced by Apple when it announced iOS 14 in June. For YouTube's mobile site users, it had allowed them to watch a video on Safari on top of other tasks they could do on their iPhone at the same time. However, that capability disappeared last month, except for those with YouTube Premium subscriptions.
Now, YouTube's mobile website appears to be supporting the native PiP mode on iOS 14 once again even if you don't have a Premium account. You can turn it on by expanding a video into a full screen view and then tapping on the small PiP icon on the top-left corner. You can then minimize Safari and open other apps while the YouTube video plays in a small window. The feature also works on non-Apple browsers including Chrome and Firefox.
That said, picture-in-picture remains unavailable on YouTube's mobile app since it must be explicitly enabled by the app itself. There have been rumors, though, that this capability was recently tested on the video sharing platform's iOS app. For now, iOS 14 users will have to settle with playing YouTube videos in PiP mode on its mobile website.