ObservableObjectInApp.swift

import SwiftUI

class DemoModel : ObservableObject {
    
    enum State {
        case value(Date)
    }
    
    @Published var counter = 0
    @Published var state = State.value(Date())
    
}

@main
struct ObservableObjectInApp: App {
    
    @StateObject var model = DemoModel()
    
    var body: some Scene {
        WindowGroup {
            VStack {
                Button("Increment \(model.counter)") {
                    model.counter += 1
                }
                Button("Update \(String(describing: model.state))") {
                    model.state = .value(Date())
                }
            }
        }
    }
}