MacOS SwiftUI: remove titlebar, include windows tabs - HSplitView paints above tabs?

Question

When removing the window titlebar it makes sense that I can paint to the top of the window.
However with the window tab bar showing, the HSplitView doesn't stop at the window tab but goes straight over it.

How do I have the HSplitView stop at the bottom of the tab?
The issue is

TestApp.swift
@main
struct TestApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
        .windowStyle(HiddenTitleBarWindowStyle())
    }
}

ContentView.swift
struct ContentView: View {
    var body: some View {
        NavigationView {
            Text("Sidebar")
            HSplitView {
                Text("left")
                    .frame(maxWidth: .infinity, maxHeight: .infinity)
                    .navigationTitle("tab name")
                Text("right")
                    .frame(maxWidth: .infinity, maxHeight: .infinity)
            }
            .toolbar {
                Button(action: {}){
                    Image(systemName: "arrow.triangle.turn.up.right.diamond")
                    Text("Button 1")
                }
            }
        }
    }
}

Result (HSplitView goes all the way to the top of the window):

2 possible solutions that feel inadequate are

struct ContentView: View {
    var body: some View {
        NavigationView {
            Text("Sidebar")
            VStack(spacing: 0) {
                Divider()
                HSplitView {
                    Text("left")
                        .frame(maxWidth: .infinity, maxHeight: .infinity)
                        .navigationTitle("tab name")
                    Text("right")
                        .frame(maxWidth: .infinity, maxHeight: .infinity)
                }
                .toolbar {
                    Button(action: {}){
                        Image(systemName: "arrow.triangle.turn.up.right.diamond")
                        Text("Button 1")
                    }
                }
            }
        }
    }
}

Which results in this (however I don't want a divider below the tabs):

OR

struct ContentView: View {
    var body: some View {
        NavigationView {
            Text("Sidebar")
            VStack(spacing: 0) {
                VStack {}
                .frame(maxWidth: .infinity, maxHeight: 1)
                HSplitView {
                    Text("left")
                        .frame(maxWidth: .infinity, maxHeight: .infinity)
                        .navigationTitle("tab name")
                    Text("right")
                        .frame(maxWidth: .infinity, maxHeight: .infinity)
                }
                .toolbar {
                    Button(action: {}){
                        Image(systemName: "arrow.triangle.turn.up.right.diamond")
                        Text("Button 1")
                    }
                }
            }
        }
    }
}

Which results in this (but I wonder if this is "accidentally" working):