How I show form on top of windows without stealing focus

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C#

In C# WinForms I am trying to create proof of concept. Trying to bring a window on top of other windows without stealing the input focus from what the user was doing before the window came up. Let say user is typing an email, and my form will come up covering email partially or fully, the user should still be able to continue typing an email (obviously user may not see what he /she is typing but still...)

I tried a few things below, could not achieve desired effect.

What I have tried:

public partial class Form1 : Form
    {
        private const int SW_SHOWNA = 4;
        [System.Runtime.InteropServices.DllImport("user32.dll")]
        private static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);

        private Timer timer;

        public Form1()
        {
            InitializeComponent();
            timer = new Timer();
            timer.Interval = 2000;

            timer.Tick += Timer_Tick;
            timer.Enabled = true;
        }

        private void Timer_Tick(object sender, EventArgs e)
        {
            Console.WriteLine("Raised: {0}", e.ToString());
            
            //this.Visible = true;
            //this.BringToFront();
            this.Activate();
            ShowWindow(this.Handle, SW_SHOWNA);
            //this.Show();
        }

        protected override bool ShowWithoutActivation
        {
            get { return true; }
        }