YouTube Restores iOS 14 Picture in Picture Capability on Mobile Website
This is an apparent reversal of a change that YouTube explicitly made following the release of iOS 14 which blocked such behavior. At that time, YouTube would only allow that capability for users with Premium accounts. Tonight's change means that any YouTube visitor can use Picture in Picture in Safari.
iOS 14 introduced native Picture in Picture capability to the iPhone for the first time, however, apps have to explicitly support the feature. YouTube's native app has never supported Picture in Picture for any of its users even though iPadOS has offered the capability for some time. There have been reports that YouTube has been testing this feature, but there have been no announcements.
As a result, iOS 14 users have had to resort to using YouTube in Safari as a workaround. Since there have been no announcements either way, it's unclear if this change is permanent or not.