After a recent update Microsoft Teams meetings are automatically generated for users who select the New Meeting option in Outlook.
To disable the Teams portion of the meeting you can select the Teams Meeting option from the top of the window then select Don't Host Online.
Alternatively, if you would like to disable the Microsoft Teams add in you can do so by going to File>Options>Add-ins. Next to Manage be sure COM Add-ins is selected then hit Go.
To disable the add-in uncheck the box next to Microsoft Teams Meeting Add-in and click Ok.
This option will completely disable the Microsoft Teams Add-in from Outlook however you can still create a Teams Meeting from within the Microsoft Teams Application.
