Much like my learned Colleague @Barney-15E
I too have as per below image including the " Purgatory " folder
Further, that folder in empty as per second image below
If I may go a little sideways User wrote " Can I use iCloud for backups and synchronizations without using iCloud Drive? "
Perhaps the reason the Purgatory files on your machine is so large is because you are syncing something like iPhone to the computer over a Direct Cabled Connection
I can not speak to that as I do not sync my iPhone to computer but to iCloud

