I have disappointing news for you, the link you included is for UIKit, not AppKit. In other words, apparently iOS may have some sort of support for duplex, but this text does not apply to the Mac (except possibly for Catalyst apps). Here is the equivalent documentation page for the Mac:
As you can see, no mention of duplex. FYI, Panorama already uses the NSPrintInfo in various info( functions and the printtopdf statement. Believe me, I’ve extracted every documented morsel out of this API method.
I guess this underscores your point of how difficult it is to find information about APIs. I consider crafting good google searches to be a fundamental skill for programmers today. Usually you try one search, then that gives you an idea for another, then another, until hopefully you find what you’re looking for. But it’s not always a happy ending.