I just had this, for me it turned out that I needed to connect via cable to my Mac first, problem was I was using a third party cable.
As a last ditched effort I dug out my apple cable (usbc-usbc)
That did the trick I got all the prompts for trusting the device and then the Developer Mode option popup in the settings.
Topic:
Developer Tools & Services
SubTopic:
Xcode
Tags: