Same problem here my 2020 Mac Mini M1. I've logged out of and logging back into my Apple ID account (multiple times). I've disabled and re-enabled my iCloud Drive (multiple times). I've even reinstalled macOS Big Sur. Two weeks ago I spent an hour + via Apple Care chat with no resolution. I'm convinced it's a software issue affecting certain Macs. I hope Apple finds a fix and soon. It's frustrating as hell that I can upload documents or see my iCloud Drive docs from my other devices.
bleedsblue89
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