iCloud Drive says it's syncing Desktop & Documents but it's not ... why? Upgraded to a new iMac because my 2011 won't take new OS's. Still runs like a champ tough. Migration generally went well from 10.13 to new iMac's 10.14 with one glaring exception, per the subject query. Decided to let it go, spend a day doing all the other manual migration and verification steps, and upgrade to 10.15 Catalina guessing it might fix it. Nope.

Googled my fanny off. Found the best info on this forum and an excellent posting from Jacob Ford. My symptoms are different. System Preferences and Finder all behave fine. I followed the reset permissions advice, etc to no avail. My iPhone, iPad and iCloud.com don't reflect my new iMac ... they're stuck in the past. I turned off iDevice and old iMac iCloud Drive Desktop and Documents syncing a couple days ago. Turned off new iMac Desktop and Documents syncing for 10 minutes or so today and then turned it back on. iMac still behaves fine but when I login to iCloud.com it says all is fine but ain't got the right files. And, System Prefs:Apple ID:Manage...:Other Documents shows very wrong size, consistent with iCloud.com

Is there a reset procedure to restart the sync down of iCloud documents on macOS?
Ta Da: Followed Andrew Swift's advice found on another forum. First I confirmed that all other devices had iCloud Drive syncing disabled. Then I checked the CloudDocs folder mentioned below and noticed that it held a couple similar entries but looking through them gave me no insights other than some were dated prior to migration and some were current ... hmm! So, I went to Terminal and typed:

killall bird
cd ~/Library/Application\ Support
rm -rf CloudDocs


and then immediately hit restart. I then double checked my mission critical software was running fine (home automation and weather station reading/posting), checked iCloud Drive in the finder and, lo and behold, I saw the desktop file list updating before my vary eyes. And the status bar at the bottom said it was copying a crapload of files &amp; GB to iCloud. I don't know how long it took but I went to bed after 8 hrs of uploading. Today I verified that iCloud.com and iDevices are all on the same wavelength. Alles ist Gut!