> Confused why it says that 'this API is not exposed'

What it says is (emphasis mine) “it’s not exposed as a public API”. In other words, Apple doesn’t provide official documentation and hooks for you to interact with the feature, like they do e.g. with Bluetooth. Even then, while they provide public APIs to interact with paired devices, interacting with the Bluetooth controller itself (e.g. turning it completely off or on) requires private APIs.