I have tried to simulate how displaying the call view on the top of all. But I have some unclear points:
Something in just swiftUI would look like this
struct AppView: View {
    
    @StateObject var callVM = CallViewModel()
    
    var body: some View {
        ZStack {
            TabView {
                Text("TabOne")
                    .tabItem {
                        Image(systemName: "list.dash")
                        Text("Menu")
                    }
                
                Text("TabTwo")
                    .tabItem {
                        Image(systemName: "square.and.pencil")
                        Text("Order")
                    }
            }
            if callVM.isIncomingCallActive {
                ZStack {
                    Color.green
                    VStack {
                        Text("Incoming call...")
                        Button(action: { callVM.isIncomingCallActive = false }) {
                            Text("Cancel")
                        }
                    }
                }.edgesIgnoringSafeArea(.all) // <= here
            }
        }
        .onAppear {
            self.callVM.getCall()
        }
    }
}
class CallViewModel: ObservableObject {
    
    @Published public var isIncomingCallActive = false
    
    func getCall() {
        DispatchQueue.main.asyncAfter(deadline: .now() + 5) {
            self.isIncomingCallActive = true
        }
    }
}