You can shoot 4k 60FPS on any of the lenses dating back to at least the 12 Pro (possibly even the 11 Pro). So if you select the 3x telephoto lens and start recording video at 4k 60fps, it will be true 3x and not a digital zoom of the 1x main lens.

There is also a "Lock Camera" setting under Camera settings that allows you to control automatic switching between lenses during recording.