Ok, I follow up on this problem.
You don't have to grab template from 2.1 to move forward on this (document is not updated yet for latest). See #15203 for more detail.
The xcode project file will be available along with
.ipa file when you hit
Export project in Godot 3.0. I knew, I don't expect such xcode project file to be generated as well as the option clearly states
.ipa. But it will be there as per user: endragor suggested in above link, and with my inspection to Godot code. Xcode project file will be generated.
Anyway, when you try to export project at of the current state in 3.0 Beta 2, you will end up like #15058. So we need to wait until the fix is there.