[jeromeof]

Well one problem I ran into was because of the changes to iTunes audiobooks are now stored in the Books app but the Books app doesn't support external drives for media so the Catalina update includes hours of copying files from my external HDD to my primary Macintosh HD - filling it up almost entirely (I have/had about 300GB of audiobooks) - this was bad enough (as their was no UI telling me it was doing this) but then Time Machine kicked in trying to back up these files (I had excluded the external drive but obviously not the primary partition) but because I ran out of space during the initial Catalina upgrade run, their were lots of artifacts which also got added to Time Machine. Time machine itself started trashing for hours.

I lost probably a day (to a day and a half tidying things up and cleaning up stuff that was not my fault) and of course I have no decent way of managing audiobooks now.