PARTIAL SOLUTION - Thank God - I don't know why this is - PGMusic might want to look at it - - - I was finally able to save my .SGU file - BUT -now it will only save to the BIAB folder. It will not save to the Desktop. It will not save to the peripheral drive, it will not save to the "HD" (Hard Drive) - it will only go into the BIAB folder.
How BIAB changed this I have no idea - but whatever it is (and it resides on the peripheral drive) it changed the setting on my Mac Mini too - and like I said, even if I disconnect the peripheral drive COMPLETELY from the Mac Mini and use my legacy BIAB 2015 or 2016 that is on my Mini's Hard drive I still get the "Error: Cannot save to root of drive" - so whatever this thing is, it acted like a worm and got into all of my BIAB stuff and drives.

Strange, everything was working fine for the past three days....go figure.