Hi @Megan,
Based on my test, the attendees would be able to unmute themselves once they are added to breakout rooms.
Please see the following screenshots:
1.in meeting options disable camera and mic for attendees
2.when user01 joins meeting, his camera and mic will be disabled and need to be allowed by organizer
3.create two breakout rooms and assign user01 to one of them
4.from user01 view he can unmute himself in the breakout room (sorry I didn't have a camera connected in my lab)
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