What audio sample rates and bit depths are supported by the iPhone X and new iPhone 12?

In the past (with analog headphones) I have checked an option in iTunes which converted high-res audio files in my iTunes (now Music) directory to lower bit rates for my iPhone. In a world where more often than not the iPhone is outputting a digital PCM stream to an external DAC (AirPods, Control4 system, CarPlay, audio receiver etc) I'm wondering what the maximum sample rate and bit depth the iPhone can store/stream/handle.

Also, do accessories like the Belkin Lightning to Headphone Jack/Charging port contain a DAC? I understand the iPhone only sends a digital (eg LPCM) signal from its lightning port.