Are you running macOS 10.15 and trying to build a SwiftUI user interface visually? Are you having trouble finding the SwiftUI user interface elements, the SwiftUI equivalent of Xcode’s object library for storyboards?
When you click the Add button in the toolbar, Xcode shows the code snippets library instead of the view library. You must click the View Library button in the library window to access the SwiftUI views.
The View Library button is the left button in the group of five buttons in the screenshot. The canvas must be open for the View Library button to appear in the library window. Once you have access to the view library, you can drag views to the canvas and build your interface visually.