I’m asking the engineer who built the integration to weigh in on these questions:
So stay tuned for more information about that soon!
For now the Zoom button remains visible as a safeguard in case something doesn’t work right with the embed. However, we’ve discussed hiding this for the reason you describe, so we’ll keep talking about this internally to decide the best way to handle it. If you’d like, please open a Contribute > Feature request for this so we can see who else is interested in this behavior.
The Join Zoom button is visible to anonymous users, but when they click it, they will be prompted to register for an account.
No, unless you restrict the topic to a category that is only accessible to those groups. Any members who can access the topic can join the event. Again, though, if this is something you’d like us to consider changing, please open a Contribute > Feature topic!