​Ahead of Microsoft's planned adoption of New Teams for all Tenancy users by the end of March 2024, you are encouraged to try it out now, by clicking the "Try the new Teams" toggle presented within MS-Teams. 

You can use the same toggle to switch back to 'Classic Teams' if required, but be aware that this will no longer be possible in the future and that New Teams will soon become the default and only version supported by Microsoft. 

Further information on New Teams can be found here: https://learn.microsoft.com/en-us/microsoftteams/new-teams-desktop-admin