Teams Live Events now support anonymous external presenters, defined as people who don’t have Azure AD or MSA accounts. It’s a useful change because many large public meetings (the natural ground for Live Events) involve external presenters brought in because of their expertise in the meeting topic. The update is rolling out in April 2021.

https://office365itpros.com/2021/04/08/teams-live-events-support-anonymous-external-presenters/