I had uploaded to iCloud a folder of about 13GB, including thousands of files. Now I am unable to delete it because after a while iCloud says that a problem occurred and that it cannot delete the folder.

i have the same issue only i uploaded 79 gigs lol of family photos. once i realized it was iCloud drive slowing down my system i disabled it.. but now I'm stuck with the files on the cloud drive that i don't really need to have there now that I've gotten a secondary back up photo drive. i did find you can delete the files inside the folders.. its time consuming.. time i don't have and I'm sure you don't either.. you're not alone in this i can tell you that lol