If you disable this feature for a user, they can't send broadcast messages when they host or cohost. Webex provides hosts and cohosts notifications about the limitations. Mobile clients hide the broadcast menu.

1

From the customer view in https://admin.webex.com, go to Meetings > Settings, External meetings section.

To toggle the feature at the user or group level using the Control Hub templates, go to Meetings > Templates.
2

Toggle the Breakout sessions > Broadcast messages setting.