This article discusses software internally used by Apple.
Acquiring a copy without Apple's consent is illegal and may result in being scammed.
Yukon 17A508 is an InternalUI build of iOS 13, judging by the file dates, it was compiled 21 hours after WWDC 2019. It appears to be a full build and not desense, yet, on the homescreen, it appears to be desense.
This build references to an accessory called "B389", judging by leaks, this is for AirTags. It also refrences "D79" which is the codename of the iPhone SE 2020 model.