How to set the location of WPF window to the bottom right corner of desktop?

To access the desktop rectangle, you could use the Screen class - Screen.PrimaryScreen.WorkingArea property is the rectangle of your desktop.

Your WPF window has Top and Left properties as well as Width and Height, so you could set those properties relative to the desktop location.

This code works for me in WPF both with Display 100% and 125%

 private void Window_Loaded(object sender, RoutedEventArgs e)
 {
    var desktopWorkingArea = System.Windows.SystemParameters.WorkArea;
    this.Left = desktopWorkingArea.Right - this.Width;
    this.Top = desktopWorkingArea.Bottom - this.Height;
 }

In brief I use

System.Windows.SystemParameters.WorkArea

instead of

System.Windows.Forms.Screen.PrimaryScreen.WorkingArea