Another thing that might have fixed mine... I found various files and folders from a development website spread across many diffrerent random folders in my icloud. It was like I'd tried to move the website folder, but it got confused with the destination and just randomly moved files and folders anywhere in iCloud. There were also .git and .node_modules folders in there... I deleted everything i could find/identify and icloud is now syncing :)

SOLVED for me: I did 3 things that people had suggested and one of them worked. I think it was the first, one, but maybe the 2nd or 3rd... 1: Kaspersky was blocking the bird icloud sync process. Opened Kaspersky > Settings > Threats > Trusted Zone Added a number of files that iCloud sync uses so that Kaspersky ignores them: /Users/tobycosh/Library/Application Support/iCloud/ /System/Library/PrivateFrameworks/iCloudNotification.framework/ /System/Library/PrivateFrameworks/iCloudQuota.framework/ /System/Library/PrivateFrameworks/iCloudQuotaUl.framework/ /System/Library/PrivateFrameworks/iCloudSettings.framework/ /System/Library/PrivateFrameworks/iCloudDriveService.framework/ /System/Library/PrivateFrameworks/icloudMCCKit.framework/ /System/Library/PrivateFrameworks/iCloudDriveCore.framework/ /System/Library/Frameworks/CloudKit.framework/ iCloud suddenly started uploading files after months of being stuck! 2: Second Mac user logged into same iCloud account I had a second Mac user on the same laptop which was signed into the same iCloud account main Mac user account. I logged out of iCloud on the second Mac user account, then I switched to my main Mac user account, and deleted the second Mac user account completely. I don't think this is what fixed it but I know that fixed it for others... 3: Millions of tiny files to sync I had 50 folders containing website code that were full of node_modules and git folders. I removed all of them from iCloud and put them on my hard disk. Someone mentioned that the millions of files slowed down iCloud sync. I'm not sure which was the correct solution, but something worked... hallelujah!!