How to replace topLeading menu bar on NavigationSplitView with TabView

I try to replace the default menu bar item. but this code still shows two button items.

import SwiftUI

@available(watchOS 10.0, *)
struct TabViewPreview<Content: View>: View {
    let content: Content

    init(@ViewBuilder content: () -> Content) {
        self.content = content()
    }

    @State private var selection: String? = "preview"

    var body: some View {
        NavigationSplitView {
            List(selection: $selection) {
                Text("preview").tag("preview")
            }
        } detail: {
            TabView {
                content
            }
            .toolbar(content: {
                ToolbarItem(placement: .topBarLeading) {
                    Button(action: {}) {
                        Image(systemName: "shared.with.you")
                    }
                }
            })
            .tabViewStyle(.verticalPage)
        }
    }
}

@available(watchOS 10.0, *)
#Preview {
    TabViewPreview {
        Text("A")
    }
}