SwiftUI MacOS app : toggle binding to modelView in subviews do not work

My main ContentView contains a ChecklistView, which contains several CheckViews, which contains a Toggle view. When clicking on a checkbox, the information is passed to the ContentViewModel, but does not come back to the subViews. How can I fix that? I'am using Xcode 16.3, with Swift 5 or Swift 6 : no difference. The joined code is designed to test different structures of view declaration.

import SwiftUI
@main
struct TestCheckListApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView(cvm: ContentViewModel())
        }
    }
}

import SwiftUI
final class ChecklistItem: Identifiable, ObservableObject
{
    let id = UUID()
    var title: String
    var isChecked: Bool
    
    init(title: String, isChecked: Bool = false) {
        self.title = title
        self.isChecked = isChecked
    }
    func toggle() { isChecked.toggle() }
}

import SwiftUI
final class ContentViewModel: ObservableObject {
    @Published var report: String = ""
    @Published var arrItem: [ChecklistItem] = [
        ChecklistItem(title: "Item 0"),
        ChecklistItem(title: "Item 1"),
        ChecklistItem(title: "Item 2")
    ]
    func buttonTapped()
    {
        var s: String = ""
        for item in arrItem
        {
            s += "\(item.title) : \(item.isChecked), "
            print("\(item.title) : \(item.isChecked)")
        }
        report = s
    }
}

import SwiftUI
struct ContentView: View {
    @ObservedObject var cvm: ContentViewModel
    @State private var multiSelection = Set<UUID>()
    var body: some View {
        VStack(alignment: .leading) {
            HStack {
                Button(action: cvm.buttonTapped) {
                    Text("Display values in view model")
                }
                Text(cvm.report)
            }
            Divider()
            HStack {
                Text("Toggles in ContentView:")
                Toggle(cvm.arrItem[0].title, isOn: $cvm.arrItem[0].isChecked)
                Toggle(cvm.arrItem[1].title, isOn: $cvm.arrItem[1].isChecked)
                Toggle(cvm.arrItem[2].title, isOn: $cvm.arrItem[2].isChecked)
            }
            Divider()
            HStack {
                Text("Toggles in CheckView in ContentView:")
                CheckView(cli: cvm.arrItem[0])
                CheckView(cli: cvm.arrItem[1])
                CheckView(cli: cvm.arrItem[2])
            }
            Divider()
            Text("Toggles in List in ContentView:")
            List {
                ForEach($cvm.arrItem) { item in
                    Toggle("item.title", isOn: item.isChecked)                    }
            }
            Divider()
            Text("Toggles in ChecklistView:")
            ChecklistView(cl: cvm.arrItem)
        }
        .padding()
        .preferredColorScheme(.light)
    }
}
#Preview {
    ContentView(cvm: ContentViewModel())
}

import SwiftUI
struct CheckView: View {
    @ObservedObject var cli: ChecklistItem
    var body: some View {
        Toggle(cli.title, isOn: $cli.isChecked)
    }
}

#Preview {
    CheckView(cli: ContentViewModel().arrItem[0])
}

import SwiftUI
struct ChecklistView : View {
    var cl: [ChecklistItem]
    var body: some View {
        List {
            ForEach(cl) { item in
                CheckView(cli: item)
            }
        }
    }
}
#Preview {
    ChecklistView(cl: ContentViewModel().arrItem)
}

If you really want to keep using final class ContentViewModel: ObservableObject, then change your final class ChecklistItem to a struct ChecklistItem and ensure you pass a binding when you want to change it. Also you need to declare a single source of data truth for your ContentViewModel.

Example code, tested on real device, not Previews:

@main
struct TestCheckListApp: App {
    @StateObject private var cvm = ContentViewModel()  // <-- here
    
    var body: some Scene {
        WindowGroup {
            ContentView(cvm: cvm)  // <-- here
        }
    }
}

struct ChecklistItem: Identifiable {  // <-- here
    let id = UUID()
    var title: String
    var isChecked: Bool
    
    init(title: String, isChecked: Bool = false) {
        self.title = title
        self.isChecked = isChecked
    }
}

final class ContentViewModel: ObservableObject {
    @Published var report: String = ""
    @Published var arrItem: [ChecklistItem] = [
        ChecklistItem(title: "Item 0"),
        ChecklistItem(title: "Item 1"),
        ChecklistItem(title: "Item 2")
    ]
    
    func buttonTapped()
    {
        var s: String = ""
        for item in arrItem
        {
            s += "\(item.title) : \(item.isChecked), "
            print("\(item.title) : \(item.isChecked)")
        }
        report = s
    }
}

struct ContentView: View {
    @ObservedObject var cvm: ContentViewModel
    @State private var multiSelection = Set<UUID>()
    
    var body: some View {
        VStack(alignment: .leading) {
            HStack {
                Button(action: cvm.buttonTapped) {
                    Text("Display values in view model")
                }
                Text(cvm.report)
            }
            Divider()
            HStack {
                Text("Toggles in ContentView:")
                Toggle(cvm.arrItem[0].title, isOn: $cvm.arrItem[0].isChecked)
                Toggle(cvm.arrItem[1].title, isOn: $cvm.arrItem[1].isChecked)
                Toggle(cvm.arrItem[2].title, isOn: $cvm.arrItem[2].isChecked)
            }
            Divider()
            HStack {
                Text("Toggles in CheckView in ContentView:")
                CheckView(cli: $cvm.arrItem[0])  // <-- here
                CheckView(cli: $cvm.arrItem[1])
                CheckView(cli: $cvm.arrItem[2])
            }
            Divider()
            Text("Toggles in List in ContentView:")
            List {
                ForEach($cvm.arrItem) { $item in  // <-- here
                    Toggle("item.title", isOn: $item.isChecked)  // <-- here
                }
            }
            Divider()
            Text("Toggles in ChecklistView:")
            ChecklistView(cl: $cvm.arrItem)  // <-- here
        }
        .padding()
        .preferredColorScheme(.light)
    }
}

struct CheckView: View {
    @Binding var cli: ChecklistItem  // <-- here

    var body: some View {
        Toggle(cli.title, isOn: $cli.isChecked)  // <-- here
    }
}

struct ChecklistView : View {
    @Binding var cl: [ChecklistItem]  // <-- here
    
    var body: some View {
        List {
            ForEach($cl) { $item in  // <-- here
                CheckView(cli: $item)  // <-- here
            }
        }
    }
}