When I go to system settings<Apple ID, the sidebar has my name under it says "Apple ID".
The page has my name under the photo circle. Under my name, it has my Apple ID (my email address).
Under it has the tab for Name, Phone, Email
Then tab Password & Security
Then tab Payment & Shipping
Then tab Media & Purchases
Devices
Then tab which says, "Failed to load devices"
Under that it has the tab Sign Out.
(Sorry I can't figure out how to screen shot and put it here in the short amount of time that I have.)
I think after I originally hit the Sign Out button the first time, I did something to try to undo my action, I think I restarted the computer. I suspect whatever I did it interfered with the complete sign out??? which is why it says Failed to load devices.
As per your suggestion, I have already shut down and restarted the iMac several times and the Sign Out button has remained.
On my iPhone, when I look at the Apple ID page, it shows this iMac under Devices. So, according to the phone, this iMac is still connected to my Apple ID. However, this iMac is definitely not getting iCloud -- none of my calendar notifications are coming are coming through.
Should I try Signing Out again, then trying the steps above?