I use an iMac running macos High Sierra. I was trying to do something with my Documents folder and I turned off iCloud on my "Desktop and Documents" by unchecking the box in the System Preferences/icloud/option window as shown below.
Once I finished I wanted to turn iCloud back on by clicking the above checkbox. However, it will not turn back on. When I click on the checkbox the checkmark appears as shown below and a message saying "Setting Up..." appears.
But if I close System Preferences and then reopen them, the checkmark is gone. Can someone tell me how to turn iCloud on for "Desktop and Documents"