Check out example codes for "swiftui present new view". It will help you in understanding the concepts better.

Code Example 1

// To show a modal (iOS 13 style), You just need a simple sheet with the ability to dismiss itself:

struct ModalView: View {
    @Binding var presentedAsModal: Bool
    var body: some View {
        Button("dismiss") { self.presentedAsModal = false }
    }
}
// And present it like:

struct ContentView: View {
    @State var presentingModal = false

    var body: some View {
        Button("Present") { self.presentingModal = true }
        .sheet(isPresented: $presentingModal) { ModalView(presentedAsModal: self.$presentingModal) }
    }
}

// Note that I passed the presentingModal to the modal so you can dismiss it from the modal itself, but you can get rid of it.
// To make it REALLY present fullscreen (Not just visually)
// You need to access to the ViewController. So you need some helper containers and environment stuff:

struct ViewControllerHolder {
    weak var value: UIViewController?
}

struct ViewControllerKey: EnvironmentKey {
    static var defaultValue: ViewControllerHolder {
        return ViewControllerHolder(value: UIApplication.shared.windows.first?.rootViewController)

    }
}

extension EnvironmentValues {
    var viewController: UIViewController? {
        get { return self[ViewControllerKey.self].value }
        set { self[ViewControllerKey.self].value = newValue }
    }
}

//Then you should use implement this extension:

extension UIViewController {
    func present<Content: View>(style: UIModalPresentationStyle = .automatic, @ViewBuilder builder: () -> Content) {
        let toPresent = UIHostingController(rootView: AnyView(EmptyView()))
        toPresent.modalPresentationStyle = style
        toPresent.rootView = AnyView(
            builder()
                .environment(\.viewController, toPresent)
        )
        self.present(toPresent, animated: true, completion: nil)
    }
}

// Finally you can make it fullscreen like:

struct ContentView: View {
    @Environment(\.viewController) private var viewControllerHolder: UIViewController?

    var body: some View {
        Button("Login") {
            self.viewControllerHolder?.present(style: .fullScreen) {
                Text("Main") // Or any other view you like
            }
        }
    }
}

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