I started a project targeting macOS and used Storyboard app lifecycle. I also used Xcode Previews in this project.
If I:
- Keep the entry point of the main storyboard to a window controller. (as default setup in macOS),
- Turn the Xcode window into full-screen,
That window controller would pop up its window every time Xcode Previews refreshes.
I tested in Xcode 26.3 RC and many versions before.