I had the same problem a few days ago.
The problem is, that Adobe normaly erases the old Illustrator-Versions when you update to a new version.
But luckily I had an Illustrator 2015 on my old laptop.
So I installed that old version on my 27" mac again.
Now there are two ways to work:
a) You design your graphic on the old version
b) You design on Illu 2020, then import it into the old version (e.g. Illu 2015) and this file you can import to RDWorks