I also was stuck on the "uploading x items to iCloud" problem for Documents and Desktop items (not photos). (If you see iCloud in your finder window Sidebar, then click on the little i in the circle, you'll see that popup.
To solve this, go to the iCloud System preference, then iCloud Drive "Options", then uncheck "Desktop and Documents Folders". It will warn you that unchecking the box will remove the items in those folders from your Mac ⚠, but that they'll be saved in your online iCloud. It will ask verification to "Turn Off". It then gives you the option to Archive all of the items in those two folders, which is what you want to do. A folder called "iCloud Drive (Archive)"is created in your Home folder. You want to chose that option because you then really haven't deleted those items from your Mac (their not even compressed), and they are recovered more quickly when you then turn the "syncing" (as some have referred to it here) back on. (I'm not really sure they are recovered from that folder, but it was quick enough that I believe that's what happened, rather then re-downloading them from my online iCloud.) The "iCloud Drive (Archive)" folder doesn't automatically disappear after reactivating "syncing", so once you've verified the Desktop and Documents folders have been "replenished" again, you can delete the Archive folder manually.