View isn't updating with zIndex in ForEach

TestView.swift

import SwiftUI

struct TestItemView: View {
  
  @State var dragAmount = CGSize.zero
  
  let letter: String
  
  var body: some View {
    Image(systemName: "\(letter).square")
      .offset(dragAmount)
//      .zIndex(dragAmount == .zero ? 0 : 1)
      .gesture(
        DragGesture()
          .onChanged({
            self.dragAmount = CGSize(width: $0.translation.width,
                                     height: $0.translation.height)
          })
          .onEnded({ _ in
            self.dragAmount = .zero
          })
    )
  }
}

struct TestView: View {
  
  @State var letters = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k"]
  
  var body: some View {
    HStack {
      ForEach(0..<10) { number in
        // Letters doesn't update inside TextItemView after updating in the onAppear method
        // if there is the zStack modifier on the TestItemView object
        TestItemView(letter: self.letters[number])
      }
    }
    .onAppear {
      self.letters = (0...10).map { _ in self.randomLetter() }
    }
  }
  
  private func randomLetter() -> String {
    String("ABCDEFGHIJKLMMNOPQRSTUVWXYZ".randomElement()!)
      .lowercased()
  }
}

struct TestView_Previews: PreviewProvider {
  static var previews: some View {
    TestView()
  }
}

Hello there
I am having the same problem now. Did you find any solution?