https://www.bleepingcomputer.com/news/microsoft/microsoft-outlook-is-disabling-teams-meeting-add-in-how-to-fix/

Microsoft is investigating a known issue affecting Outlook for Microsoft 365 users and preventing them from creating Teams meetings using the app's ribbon menu.

The Teams Meeting add-in, as its name says, can be found in the Calendar view and it enables Outlook users to schedule a Teams meeting from Outlook.