Msdminiplayer -

: While a video is playing, swipe up or press the home button to exit the app. The video should shrink into a floating window on your home screen.

: Touch and drag the player to move it anywhere on your screen. You can often pinch-to-zoom or double-tap the window to change its size. MSDMiniplayer

: If it isn't working, check your device settings under Apps > Special app access > Picture-in-picture (Android) or Settings > General > Picture in Picture (iOS) to ensure the feature is enabled. How To Turn On Miniplayer On YouTube - Step By Step : While a video is playing, swipe up