From Xojo Documentation
Removes the focus from the control that has the focus, leaving no control with the focus. On Windows only, the app also no longer receives KeyDown events.
After calling this method on Windows, the app no longer receives Keydown events. Use Window.SetFocus if your app needs to continue to receive KeyDown events.
You can set the focus to a specific control using the SetFocus method of the RectControl class.
The following code in the Action event of a PushButton removes the focus from the object in the window that has the focus, leaving no control with the focus until the user selects or clicks in a control that can get the focus.