Just as a follow-up, the above procedure described by George may have worked. I tried multiple times to unconfigure the Solidworks Workbench plugin for both "all users" and "current user (admin)". Every time I relaunched the CAD Configuration Manager, it appeared to reselect the "Workbench Associative Interface" radio button option, but I was able to get the Solidworks 2021 licensing requests to stop. The situation seemed a little shaky though, so I went ahead and temporarily uninstalled Solidworks 2021 to make sure Solidworks 2020 would be used for the geometry update.

Thanks for your help George!