https://learn.microsoft.com/en-us/windows/windows-app-sdk/api/winrt/microsoft.ui.xaml.input.focusmanagerlostfocuseventargs?view=windows-app-sdk-1.5
FocusManagerLostFocusEventArgs Class (Microsoft.UI.Xaml.Input) - Windows App SDK | Microsoft Learn
Provides data for the LostFocus event.
windows appclassmicrosoftuixaml