iCloud Password and Photos sync issues after MacBook Tahoe upgrade

After upgrading my MacBook to Tahoe password sync is turned off in iCloud settings. It was working before the upgrade, it has the latest changes that the other devices have. Now the slider to turn it on indicates it is off and trying to turn it on only results in a spinner that disappears after a few seconds.

I have tried to sign out of iCloud and that warns me that it will delete 3500 images - which is totally unwanted, unneeded, and unexpected - but otherwise it will not try to sign out. When I finally gave up and told it to go ahead it refused to stop because it is still syncing photos and ignores any attempt to tell it to stop. It says "Your iCloud Photos is (sic) currently updating. " It offers buttons to Continue Updating" or "Turn Off". If I select the "Turn Off" button it changes the System Settings display to "logging out" and hangs up. That inhibits a restart, requiring me to quit the settings app to proceed, but it refuses to quit because it is still updating.

The only way out that loop is to force a power off.

There should not be any pending changes to any synced data and it has been in the state since last night. It says it is updating photos, but if it is, it is doing it without generating any network traffic. Nothing iCloud related is using any data in Activity Monitor. It is connected to the internet.

Has anyone had this issue - and better yet - managed to fix it? I am out of ideas.

[Re-Titled by Moderator]

Original Title: ICloud Sync broken after Tahoe upgrade, attempting to log of iCloud out locks up Settings App.