Hello and welcome to Apple Support Communities, anneliefrombrackenfell.
If I understand your post correctly, you are getting a warning message that your iCloud Drive is full and that documents are taking up most of the space but you show less than half of the space being used by documents in Finder. It's important to know how much space you still have available. I'd like to help.
First, restart your Mac and then take a look at the iCloud Storage directly by clicking on the Apple () menu > System Preferences, and iCloud, then click Manage. If the storage amount still appear off here, check to see if the recently deleted files are still being counted toward the total:
When you turn on iCloud Drive, any documents that you already store in iCloud automatically move to iCloud Drive. You can see your files on iCloud.com, in the Files app on iOS 11 and later, in the Pages, Numbers, and Keynote apps, or in the iCloud Drive app on iOS 10 and iOS 9.
If you don’t see your files in any of those locations, make sure that you set up iCloud Drive on all of your devices. If you don't see the files from your Mac Desktop and Documents folder on iCloud.com, go to System Preferences > iCloud, then click Options next to iCloud Drive and make sure that it's turned on.
If you need to access a file that you deleted within the last 30 days, you can get it back from the Recently Deleted folder in the Files app, or on iCloud.com. After 30 days, your files are removed from Recently Deleted.
- Open the Files app on your iPhone, iPad, or iPod touch.
- Go to Locations > Recently Deleted.
- Select the file that you want to keep.
- Tap Recover.
- Sign in to iCloud.com from your Mac or PC.
- Go to iCloud Drive and click Recently Deleted items in the bottom-right corner.
- Select the file that you want to keep.
- Tap Recover.
- Go to Trash.
- Select the file that you want to keep.
- Control-click, then choose Put Back. Or you can drag the file back to your desktop or iCloud Drive.
See the full article here:
Get help with iCloud Drive
Let us know if that resolves this issue for you.
Thanks for using the Apple Support Communities. Take care.