Has anyone managed to get this working?

I'm 99% of the way there and have the three column split view working fine, however if one of the tabs is a NavigationView for some reason that tab displays as a two column split view.

In the example below, Tab 3 is a NavigationView and exibits the above problem.

extension UISplitViewController {
    open override func viewDidLoad() {
        preferredDisplayMode = .twoBesideSecondary
        preferredSplitBehavior = .tile
    }
}

struct ContentView: View {

    var body: some View {
        TabView {
            NavigationView {
                Text("ColumnOne").navigationBarTitle("ColumnOne", displayMode: .inline)
                Text("ColumnTwo").navigationBarTitle("ColumnTwo", displayMode: .inline)
                Text("ColumnThree").navigationBarTitle("ColumnThree", displayMode: .inline)
            }
            .tabItem {
                Label("Tab 1", systemImage: "list.dash")
            }
            Text("Tab 2")
            .tabItem {
                Label("Tab 2", systemImage: "list.dash")
            }
            NavigationView {
                Text("Tab 3")
            }
            .tabItem {
                Label("Tab 3", systemImage: "list.dash")
            }
        }
    }
}

If you do not want that then add this modifier to Tab 3 NavigationView and then it will only show one view

.navigationViewStyle(StackNavigationViewStyle())