What I would recommend is to focus on the behavior of your feature when you write a scenario, not the frontend interaction. If you want to know more about BDD, I would also recommend to check out Cucumber school and our blog.
This is what I would do to write the scenario but be aware that it is based on my understanding.
Given a user is authenticated as Super Admin
When I add a user to another hub (do not care in the scenario if it is a drop-down or radio buttons, or something else, just focus on the action)
Then only hubs that to do not include the user are available (no datatable here. Programatically, you can just check that you do not display the hubs including the user)
The fact that “organization contains these hubs” and “there is a user who belongs to this hub” are not required since they do not bring anything to the behavior which should be true in any case.
I hope it helps. You are on a good track! Happy testing!!!