Program.cs

using System.Security.Principal;

namespace tray_monitor;

static class Program
{
    /// <summary>
    ///  The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main()
    {
        if(IsAdministrator()) {
            // To customize application configuration such as set high DPI settings or default font,
            // see https://aka.ms/applicationconfiguration.
            ApplicationConfiguration.Initialize();
            Application.Run(new TrayApp());
        } else {
            MessageBox.Show("This application needs to be run as administrator.", "Erro", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
    }    

    private static bool IsAdministrator()
    {
        WindowsIdentity identity = WindowsIdentity.GetCurrent();
        WindowsPrincipal principal = new WindowsPrincipal(identity);
        return principal.IsInRole(WindowsBuiltInRole.Administrator);
    }
}