The new Teams Calendar app gets a new feature called Meet Now to create on-demand or ad-hoc meetings that don’t need to be scheduled in anyone’s calendar. There doesn’t seem to be any reason not to allow users to use Meet Now, but if you need to block the feature, you can edit a Teams meeting policy and assign it to the unfortunate users.
https://office365itpros.com/2019/09/03/new-teams-calendar-app-meet-now-feature/
