Additional features, settings, or issues not covered by specific Microsoft Teams categories
Hi Wendy,
Thanks for posting back.
According to the reference: Hardware requirements for Teams on a Mac, the Operating system is required Mac OS X 10.11 El Capitan or later one of the three most recent versions of macOS (you'd better view the reference to get the latest information). Please update your system, OR you could use Teams for Web to instead. Sorry for the inconvenience happens to you.
Regards,
George