Hi @Paul Sparke
The share button for webinars is by design and cannot currently be turned off from settings.
If the organizer doesn't want other external users to enter the webinar through the link, you can set the meeting so that only users within the organization can join.
If the organizer has to create a public webinar, you can restrict the ‘Who can bypass the lobby?’ feature. Some users you don't want to enter the meeting will be in the lobby waiting for your approval to enter the meeting.
Meanwhile,To get this feature more quickly, you can send a feedback directly to Microsoft Feedback to add it in future updates.
Many features of our current products are designed and upgraded based on customers’ feedback. With requirements like this increase, the problem may well be released in the future.
Thanks for your understanding and support.
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