According to Android Police, YouTube introduced a new feature called pinch to zoom exclusively for Premium users. The feature allows users to zoom and users can zoom different parts of the screen, both in portrait or full-screen landscape view.
If you’re using YouTube Premium, you can try this feature through setting menu “Your Premium benefits,” tap “Try new features” section, and enabling the zoom feature. This may take a while, but once it’s activated, you can zoom in at up to 8x.
Previously, YouTube tested a picture-in-picture with random users and beta app testers. In 2020, the picture-in-picture feature will come for Premium users. Some benefits come to Premium users, including playlist management and browser-based voice search. Zoom feature will be available until September 1st, and it’s only available for Android devices for now.