The MS Teams app is available for MacOS, iOS, and iPadOS.
But there may be occasions when you wish to use a web browser to connect to teams.microsoft.com — for example, to bring up a 2nd instance of MS Teams, in addition to the Teams app you are using. But if you connect to teams.microsoft.com using MacOS’ default Safari browser, you’ll see this message.
But you can connect to teams.microsoft.com by selecting a different browser, such as Microsoft’s Edge browser, which is available for MacOS.