Hi, no joy. First, I mention that Alfred had been able to add the collection to the file, so it was able to modify.
It turns out my preferences file was in the top level of the Dropbox folder. There was also an "Alfred" folder with an old preferences file, and a Dropbox (Archive) folder on my hard drive (from the Ventura changes to Dropbox, I believe) that also had an Alfred folder. with a preferences file in it I deleted the Alfred folder from the Dropbox directory and created a new empty one, and I deleted the file in the (Archive) folder. I created a new Alfred folder on Dropbox and changed the Alfred preferences to point to it. After Alfred restarted and was pointing to the new folder, I tried to delete the collection again, but I got the same error message. I then deleted the preferences file from the root of Dropbox, and I've verified that the one I just made is now the only alfredpreferences file on my Mac. I still can't delete the collection.
Any other thoughts are appreciated. Please let me know if there's anything else you'd like me to supply.