NSInvalidUnarchiveOperationException when loading the nib / storyboard means there an object in the nib / storyboard that the runtime doesn’t understand. This is because the framework that defines that kind of object is missing.
So, in this case, you need to link your app target against the WebKit framework so that the app understands what a WKWebView is when it is decoded from the storyboard.
Here’s a screen shot showing the app target’s Build Phases when this is correctly configured:
