Proof of concept of a NavigationStack not updating when a value changes

NavigationStack.swift

import SwiftUI

struct ContentView: View {
  
  @State private var foo: String? = nil

  var body: some View {
    
    // Change this to `NavigationView` and it'll work.
    NavigationStack {
      if let foo { Text(foo) }
      else { ProgressView() }
    }
    .task {
      // Simulate loading some data asynchronously.
      DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
        foo = "loaded"
      }
    }
  }
}

struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
  }
}