When you use your LoggedInView in your app you do need to provide some binding, such as an @State from a previous view or an @EnvironmentObject.
For the special case of the PreviewProvider where you just need a fixed value you can use .constant(false)
E.g.
#if DEBUG
struct LoggedInView_Previews : PreviewProvider {
static var previews: some View {
LoggedInView(dismissView: .constant(false))
}
}
#endif