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?