Topic on Talk:Divinity: Original Sin II - Definitive Edition
That's what launching the game executable directly does.
When I last looked into this a month or two ago I attempted a whole bunch of different ways of getting the game to launch without crashing/closing without GOG Galaxy running but they were all unsuccessful. This time around I am not really interested in redoing all of that so I only did some quick 5-10 minutes of testing before undoing the undo of my original edit.