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Prohibit file transmission at all meetings, including meetings held by tenants of other companies
I checked the article on pro pack for cisco webex control hub.
Article is a setting that prohibits file transfer when chatting to Webex app
(Webex Teams) products.
https://help.webex.com/en-US/article/np3c1rm/Pro-Pack-For-Control-Hub
So, Can add the same feature to webex meeting, then,Use this to prohibit WebEx file transfer for all domain users registered in your company's Active Directory