April 3rd, 2017
In Xcode 8.3 Apple removed the Use Storyboards checkbox for new Cocoa application projects. New projects use storyboards. Keep a copy of Xcode 8.2 to create new projects if you prefer using xib files.
If you want to use xib files instead of storyboards in Xcode 8.3, you’ll have to remove the storyboard from the project and add a xib file to the project. You will also have to tell Xcode to use your xib file as the main interface file for the project.
Additional information can be found in the following thread on Apple’s developer forums:
Tags: xcode 8