New Form is not shown while drag & drop a Custom Control from toolbox to Designer in WinForms in NetCore

[KarkuvelRajan]

In our Control, we have opened a new form to update the content of our control in the Designer. The new Form is not shown in the NetCore but works properly in the NetFrameWork. I have replicated the same issue in a simple control.

` [ToolboxItem(true)] // This attribute makes the control visible in the Toolbox
public class CustomButton : Button
{
// Constructor
public CustomButton()
{
// Set default properties
this.BackColor = Color.Blue;
this.ForeColor = Color.White;
this.Text = "Custom Button";

        Form FileLoadForm = new Form();
        FileLoadForm.Controls.Add(new Button());
        FileLoadForm.ShowDialog();
    }
}`

Sample for your reference: [NetCore.zip](https://github.com/dotnet/winforms/files/15200764/NetCore.zip)