Currently I think only drag-in of files from explorer or desktop is possible when you use just the TBGL-window. So I fear there's no way to drag stuff out of TBGL-window nor to recognize a drag-out - except you have your own GUI within TBGL which would be some internal drag'n drop - or you use UI-canvas and callbacks which both doesn't have much to do with TBGL_BindWindowEvent/TBGL_OnDropFiles then.
A weird idea to get around this: save a small file onto the desktop/ into some special folder if the user clicks onto something. When the file gets dragged in you can use the data - either delete it then or leave it re-useable
Find an example here (scroll all the way down there)
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