Sounds like the op doesn't want to have to run another program to sync, but for it happen automatically. I don't know if rsync supports a "live" mode, I've only ever used it in scripts. So, assuming you don't want a cron job running in a tight rsync loop, let the vendor tools do the work for you.
I think you want iCloud and OneDrive to sync the same folder, but I think iCloud is very limited (only syncs Desktop and Documents, AFAIK). OneDrive might actually be more flexible. Create a folder on your desktop called "MyShare" or whatever. Find the folder where OneDrive syncs and make a symbolic link to MyShare, something like this:
ln -s ~/Desktop/MyShare .
OneDrive might follow the symlink and sync it up to your public OneDrive. If it doesn't work, try it the opposite way, creating the MyShare under the OneDrive folder, and then symlinking that to your Desktop.
See if this helps>>>>>>>>https://www.chriswrites.com/how-to-sync-files-and-folders-on-the-mac/
– Moab – 2020-01-28T21:12:54.573I'd also recommend rsync. If you're having trouble, if you provide some more details, I can show you how to use crontab to do it automagically. Also, have you tried soft links? It's possible OneDrive respects them. – JMY1000 – 2020-01-28T21:32:05.037