I’ve tried that but didn’t work for me. Does it work historically? Meaning it will work for all the users who are already members of both groups?
Additionally - what about having not just two but three groups? This is indeed my actual use-case, as beside course members (flair A), and inner circle members (flair B), I also have mentoring clients (flair C).
You may need to give users instructions to set group to primary in their user preferences.
Alternatively an Automation may work. However this requires some SQL knowledge to do if a script doesn’t already exist. So you may need to consider sponsoring a script for automation(this plugin is part of core) in Marketplace