Thanks for sharing. I have been using the Owncloud client for Ubuntu 20.04 as well. It works with the distribution package.
Nevertheless I had a problem when trying to add the sync of a folder shared by another user with me. In CERNBox client one enters the absolute EOS path of this extra folder and it works. Such setting is not possible with the default Ownclient.
Fortunately this time it wasn’t really hard to recompile the CERNBox client from the source available for 19.10 as reported here: https://linux-community.web.cern.ch/t/cernbox-for-ubuntu-20-04