In Teams, there may be situations where external users join a Teams meeting. If they need to be able to share their screen and cannot, the setting for external users to share their screen may be turned off. Here is how to enable it.

https://admin.teams.microsoft.com/policies/meetings/edit/R2xvYmFs

Enabled the external sharing "request control" in Teams admin center. Teams admin center -> meetings -> meeting policies -> global -> External participants can give or request control -> on