How do I monitor registry change when 'windows 10 app mode' changes

<pre>using Microsoft.Win32;
using System;
using System.Globalization;
using System.Management;
using System.Security.Principal;
using System.Windows;
using System.Windows.Media;

namespace WpfApp1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

		private const string RegistryKeyPath = @"Software\Microsoft\Windows\CurrentVersion\Themes\Personalize";
		private const string RegistryValueName = "AppsUseLightTheme";

		public void CheckRegKeyExists()
		{
			if (Registry.GetValue(RegistryValueName,RegistryValueName, null) == null)
			{
				Background = Brushes.AliceBlue;
			}
			
		}

		private enum WindowsTheme
		{
			Light,
			Dark
		}

		public void WatchTheme()
		{
			var currentUser = WindowsIdentity.GetCurrent();
			string query = string.Format(
				CultureInfo.InvariantCulture,
				@"SELECT * FROM RegistryValueChangeEvent WHERE Hive = 'HKEY_USERS' AND KeyPath = '{0}\\{1}' AND ValueName = '{2}'",
				currentUser.User.Value,
				RegistryKeyPath.Replace(@"\", @"\\"),
				RegistryValueName);

			try
			{
				var watcher = new ManagementEventWatcher(query);
				watcher.EventArrived += (sender, args) =>
				{
					WindowsTheme newWindowsTheme = GetWindowsTheme();
					// React to new theme
					if (newWindowsTheme == WindowsTheme.Light)
					{
						Background = Brushes.WhiteSmoke;
						MessageBox.Show("Light");
					}
					else
					{
						Background = Brushes.DarkGray;
						MessageBox.Show("Dark");
					}
					
					
				};

				// Start listening for events
				watcher.Start();
			}
			catch (Exception)
			{
				// This can fail on Windows 7
			}

			WindowsTheme initialTheme = GetWindowsTheme();
		}

		private static WindowsTheme GetWindowsTheme()
		{
			using (RegistryKey key = Registry.CurrentUser.OpenSubKey(RegistryKeyPath))
			{
				object registryValueObject = key?.GetValue(RegistryValueName);
				if (registryValueObject == null)
				{
					return WindowsTheme.Light;
				}

				int registryValue = (int)registryValueObject;

				return registryValue > 0 ? WindowsTheme.Light : WindowsTheme.Dark;
			}
		}

	}
}

Original source of the above code