Is there a way to use libMobileGestalt.tbd in an Apple-approved manner?

Are there official header files for libMobileGestalt.tbd … ?

No. Mobile Gestalt is an implementation detail, not an API.

are there any substitutes for its functionality?

What are you trying to do?

Mobile Gestalt does a lot of different things, so I need more details before I can give you a definitive answer.

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

I'm trying to get a list of detailed hardware and software information, similar to what /System/Applications/Utilities/System Information.app does.