Avid Sibelius on macOS Sierra - linking folders
You just need a short script (even a single line command would work) to make a dupe of the files to your iCloud folder

Your iCloud folder is found locally on your machine in /Users/&lt; username &gt;/Library/Mobile\ Documents

(replace &lt; username > with your actual username and be certain to notice the backslash before the space in "Mobile Documents")

If you want to avoid having to preface a backslash before (a.k.a "escaping") the space, put the whole line in quotes:

"/Users/Library/&lt; username &gt;/Mobile Documents/foo.bar" 


I would use tar to create a single file archive and gzip to compress it to save space.  The command below will accomplish both:

$ tar cvfz "/Users/username/Library/Mobile Documents/Avid_Backup.tgz" "/Users/username/Library/Application Support/Avid"


You could then use Automator to run a shell script executing the command at a predetermined interval (Automator Calendar Alarm)