Vulnerability Discussion
The macOS built-in Notes.app connection to Apple's iCloud service must be disabled.
Apple's iCloud service does not provide an organization with enough control over the storage and access of data and, therefore, automated Notes synchronization must be controlled by an organization approved service.
Check
Verify the macOS system is configured to disable iCloud Notes with the following command:
/usr/bin/osascript -l JavaScript << EOS
$.NSUserDefaults.alloc.initWithSuiteName('com.apple.applicationaccess')\
.objectForKey('allowCloudNotes').js
EOS
If the result is not "false", this is a finding.
Fix
Configure the macOS system to disable iCloud Notes by installing the "com.apple.applicationaccess" configuration profile.