FYI, Interface Builder is used to build old UIKit or AppKit apps. SwiftUI has its own preview canvas built into Xcode that renders a preview of your UI and which you can then use to modify your views and have the corresponding code generated.
Yeah one of the first things I do when I start a project is get rid of that default preview code because that preview takes up too much screen space and also seems to turn itself off a lot of the time.
When I'm done learning the basics of Swift I'll check it out further + The object library.