Migrating to .NET 6 UserControl with ToolStrip does not work

Question

I'm trying to create a user control that contains multiple controls.

For example, a ToolStrip that is editable at design time(add Item a design time). The following code works in .Net Framework 4.7, but not in .NET 6.

[Designer(typeof(MyDesigner))]

public partial class AdvToolStrip : UserControl
{
    public AdvToolStrip()
    {
        InitializeComponent();
    }

    
    [Category("Appearance")]
    [DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
    public ToolStrip NewToolStrip
    {
        get { return toolStrip1; }
    }

}

public class MyDesigner : System.Windows.Forms.Design.ControlDesigner
{
    public override void Initialize(IComponent c)
    {
        base.Initialize(c);
        AdvToolStrip ctl = (AdvToolStrip)c;
        EnableDesignMode(ctl.NewToolStrip, "TS");
    }
}