Microsoft already announced that they are going to stop the support of Microsoft Apps like Teams and Services on Internet Explorer 11 (IE 11) browser by this time next year 2021.
They announced this statement on their roadmap on 17th Aug 2020.
As per that announcement,
Beginning November 30, 2020, the Microsoft Teams web app will no longer support IE 11.
Beginning August 17, 2021, the remaining Microsoft 365 apps and services will no longer support IE 11.
Hence, from November 30th, 2020 Microsoft Teams app will not work on Internet Explorer 11 which is IE 11 browser, and Microsoft recommends using new Microsoft Edge browser.
This new Microsoft Edge browser was built on Chromium open source.
Note: We may use Microsoft apps and services on IE 11 after that date, but we will have degraded user experiences with some features not available or some may cease to work.
As per Microsoft earlier announcement,
Beginning March 9, 2021, Microsoft will end the life of Microsoft Edge Legacy and will not receive security updates.
Hence, Microsoft recommends using the new Microsoft Edge browser.
Microsoft already started to ship the new Microsoft Edge and upgraded most of the Windows 10 customers to the new Edge browser.
Because they are ending support for the Microsoft Edge Legacy desktop app on March 9, 2021.
Since Chromium open source is used to build a new Microsoft Edge browser, this gives the best user experience like Google Chrome which was also built on Chromium open source.
The apps and sites that are created for Microsoft Edge Legacy will continue to work in the new Microsoft Edge.