Camera Device Selection.
Tap on a camera device selection button:

And choose the camera device/type that best suits your current photo session.
The default device/type is a wide-angle camera.
The selection options depend on the number and type of cameras in your iPhone/iPad. For example, on the iPhone 12 Pro Max, you can switch to the following:
Single Camera Device.
Ultra Wide.
Allows you to zoom out for a much larger field of view.
Wide-Angle Camera.
This is the default camera device/type used. It has probably been around since the first single-camera iPhone. Some say: “And it’s probably the lens you use the most.”
Telephoto Camera.
Allows you to zoom in for a closer view of your subject.
Note: The above options of the stock camera app correspond to the zoom switches 0.5, 1x, 2.5.
Combined Camera Device.
Dual Camera.
Probably what was available on dual-camera iPhones before the iPhone 11. That would be to take better portraits back then. I could be wrong.
Dual Wide Camera.
Combines Ultra Wide and Wide cameras. Someone taking photos inside buildings or trying to capture large objects like rocks from a short distance might find this option useful for zooming from ultra-wide to wide range.
Triple Camera.
Combines Ultra Wide, Wide, and Telephoto. An excellent option if you want the maximum zoom range in your photo session.