When using the DJI Mavic 3 Pro series there are several ways you can switch between the cameras.
If you're using the camera in Explore mode, both Picture and Video, you can use the camera control wheel to zoom in digitally from 1x to 3x, 3x to 7x, and 7x to 28x. When you scroll through the zoom digitally you only switch to a different lens when the amount of zoom reaches the next lens's optical zoom.
In all of the other photo modes: Single, AEB, Burst, and Timed Shot you can only access the optical zoom of each lens by tapping the 1, 3, and 7 on the screen in the camera view.
In video modes you can use the camera control wheel to zoom digitally or click the respective optical zoom numbers on the screen in the camera view. By selecting the zoom via tapping on the screen you automatically switch to the lens at that focal length.