Hey M.E.D,
We'd be happy to help out. We understand you're having an issue enabling iCloud Drive for your Mac.
The following details might be helpful to get started:
If you already use a feature from another cloud provider that syncs or manages your Desktop and Documents folders, you need to turn it off to use Desktop and Documents. Desktop and Documents requires macOS Sierra or later.
This is outlined further here: Set up iCloud Drive - Apple Support
We also notice you're low on storage and also have Optimize Mac Storage disabled. Perhaps you don't have enough local space to fit everything currently in iCloud Drive so enabling this feature could help reduce the amount of free space you need.
We hope this helps out.
Take care!