iOS 16's biggest new features and upgrades are highlighted by an overhauled iPhone Lock Screen, and that includes a full-screen music player and mini visualizer. With iOS 16, multiple Lock Screens can be saved on an iPhone and linked to a Home Screen, and it's easier than ever to swap them out. Holding down the Lock Screen will bring up a fresh user-interface to change Lock Screens, and swiping left and right will show saved wallpapers. The Lock Screen also brings additional customization options, such as the ability to change the clock font and add widgets.
https://screenrant.com/enable-full-screen-music-player-lock-screen-ios-16-how/