iCloud Drive not syncing

Good afternoon henrip,

Welcome to the Apple Support Communities!

I understand you are trying to synchronize the data you have on iCloud Drive across multiple devices like you are doing with Contacts. I can provide a few resources to help you with this. What version of macOS do you have on your Mac? If you have not done so already, update your computer to the most recent macOS version (currently iOS 10.14.3) Are you signed in with the same Apple ID on your Mac and all of your devices? Try quitting your current apps and restarting your iMac to refresh it and reestablish network connections.

Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch

Set up iCloud Drive

iCloud Drive FAQ

Get help with iCloud Drive

Take care.

As per this article https://support.apple.com/en-in/HT204247

If you run out of iCloud storage, your device won’t back up to iCloud, new photos and videos won't upload to iCloud Photos, and iCloud Drive, other iCloud apps, and your text messages won't stay up to date across your devices. And you can't send or receive emails with your iCloud email address. If this happens, you can make more space.

Did you unchecked the box of iCloud drive in system preferences > iCloud in front of iCloud Drive click on options button make sure desktops and documents box is checked see this articles https://support.apple.com/en-in/HT204025

https://support.apple.com/en-gb/HT206985