https://learn.microsoft.com/fr-fr/dotnet/api/system.windows.input.keyboard.previewlostkeyboardfocus?view=netframework-4.8.1&viewFallbackFrom=windowsdesktop-10.0
Keyboard.PreviewLostKeyboardFocus Attached Event (System.Windows.Input) | Microsoft Learn
Occurs when an element is in the process of losing keyboard focus.
event systemkeyboardattachedwindowsinput