iCloud unavailable?

I store a lot of my iMac on iCloud, including desktop, apps, documents (with app data files) and so on. For the entire day I have not been able to access them using OS 11.0.1 Big Sur. (I've installed 11.0 when it first came out and this is the first time I've had difficulty with it.)

I can access a lot of my documents through IOS Files, but that doesn't help with regard to MacOS-only apps like FileMaker Pro, which I use for my business.

I checked System Preferences and everything seems in order there, including System Preferences > Apple ID > iCloud > iCloud Drive > Options. Two hiccups, though: 1) several times when I check the latter, Desktop and Desktop Folders is unchecked -- but not always. When it's checked I've immediate rebooted but there doesn't seem to be any regularity with whether D&DF is or is not checked then. 2) I cannot get Keychain to check, even though I've used it for years. The checkbox itself is grayed out.

Any help would be greatly appreciated!