Thanks for the information, very interesting however I do know it is working as I can drag windows over to the display when activated as an additional temporary display. But what I need to know is how to disconnect this display when I no longer use it as an additional display with my laptop. Here is my setup. I have an old Mac mini on my desk as an additional backup running Time Machine. Was just making use of an old mini. It works well. By accident, I discovered I could use the display that is plugged into the mini and sleeping most of the day as an additional display with my laptop. My laptop is hardwired into a 32" display full-time. I use Autocad on this main display and the additional display helps to show any information I need for my Autocad drawing. Thought it might help to understand my setup, I have left my laptop in this configuration and found it doesn't go to sleep on it's own so I wanted to be able just to stop using the additional display as an extended display to my laptop. Thought clicking on the icon would work but nothing happens.
I really appreciate any advice. thanks