<telerik:RadWindow x:Class="Example.MainWindow" 
                xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
                xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
                xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation" 
                xmlns:helpers="clr-namespace:Telerik.Windows.Controls.Theming.Helpers;assembly=Telerik.Windows.Controls" 
                helpers:WindowEffectsHelper.BackdropMaterial="None" 
                Header="RadWindow"> 

<telerik:RadWindow  xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation" x:Class="Example.MainWindow"
                    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
                    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
                    xmlns:local="clr-namespace:WindowWindows11ThemeTest"
                    mc:Ignorable="d"
                    
                    Style="{DynamicResource RadWindowStyle}"
                    
                    Header="MainWindow" Height="450" Width="800">

private bool isDarkPalette;

private void RadButton_Click(object sender, RoutedEventArgs e)
{
    if (this.isDarkPalette)
    {
        Windows11Palette.LoadPreset(Windows11Palette.ColorVariation.System);
        this.isDarkPalette = false;
    }
    else
    {
        Windows11Palette.LoadPreset(Windows11Palette.ColorVariation.Dark);
        this.isDarkPalette = true;
    }

    this.MergeDictionaries();
}

private void MergeDictionaries()
{
    Application.Current.Resources.MergedDictionaries.Clear();
    Application.Current.Resources.MergedDictionaries.Add(new ResourceDictionary()
    {
        Source = new Uri("/Telerik.Windows.Themes.Windows11;component/Themes/System.Windows.xaml", UriKind.RelativeOrAbsolute)
    });
    Application.Current.Resources.MergedDictionaries.Add(new ResourceDictionary()
    {
        Source = new Uri("/Telerik.Windows.Themes.Windows11;component/Themes/Telerik.Windows.Controls.xaml", UriKind.RelativeOrAbsolute)
    });
    Application.Current.Resources.MergedDictionaries.Add(new ResourceDictionary()
    {
        Source = new Uri("/Telerik.Windows.Themes.Windows11;component/Themes/Telerik.Windows.Controls.Navigation.xaml", UriKind.RelativeOrAbsolute)
    });
}

public MainWindow() // where MainWindow is RadWindow
{
	InitializeComponent();
	SystemEvents.DisplaySettingsChanged += SystemEvents_DisplaySettingsChanged;
}

private void SystemEvents_DisplaySettingsChanged(object sender, EventArgs e)
{
	if (this.WindowState == WindowState.Maximized)
	{
		this.WindowState = WindowState.Normal;
		this.WindowState = WindowState.Maximized;
	}
}

<dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">true/PM</dpiAware>

System.EntryPointNotFoundException: Unable to find an entry point named 'GetDpiForSystem' in DLL 'User32.dll'.

   at Telerik.Windows.Controls.InternalWindow.Standard.NativeMethods.GetDpiForSystem()

   at Telerik.Windows.Controls.InternalWindow.Standard.DpiHelper.GetSystemScaleFactor()

   at Telerik.Windows.Controls.InternalWindow.Standard.DpiHelper.CalculateScaleFactor(IntPtr hwnd)

   at Telerik.Windows.Controls.InternalWindow.Standard.DpiHelper.GetPerMonitorDPIAwareScaleFactor(IntPtr hwnd)

   at Telerik.Windows.Controls.InternalWindow.ChromelessWindowHelper.<Initialize>b__81_0(Object sender, EventArgs args)

   at System.Windows.Window.OnSourceInitialized(EventArgs e)

   at System.Windows.Window.CreateSourceWindow(Boolean duringShow)

   at System.Windows.Window.CreateSourceWindowDuringShow()

   at System.Windows.Window.SafeCreateWindowDuringShow()

   at System.Windows.Window.ShowHelper(Object booleanBox)

   at System.Windows.Window.Show()

   at Telerik.Windows.Controls.InternalWindow.WindowWithNoChromeWindowHost.Open(Boolean isModal)

   at Telerik.Windows.Controls.WindowBase.ShowWindow(Boolean isModal)

   at Telerik.Windows.Controls.RadWindow.Show()

   at TelerikWpfCrash.App.OnStartup(StartupEventArgs e) in C:\Users\fedarovich\source\repos\Test\TelerikWpfCrash\TelerikWpfCrash\App.xaml.cs:line 20