I cannot add a provisioning profile to my new Phone Xs, because I updated from iOS 12.0 to 12.01 (I think)
I also found that the information screen does NOT include the iPhone UDID.
This link shows how to get it: http://www.iphonehacks.com/2018/09/how-find-iphone-xs-max-udid.html
Is anyone else having trouble with provisioning profiles and iOS12?
I managed to get Xcode 10 working by setting the environment to use Xcode 9.4.1 command line tools
Hope this helps.