This behavior is well-known issue and can be solved with some of the following procedures:
Install the Teams app as an administrator of the Windows computer.
Download, install and sign into Teams and then restart Teams and Outlook, in that order.
To ensure that the add-in is installed and loaded correctly, you may need to restart Teams and Outlook after installing. Follow these steps:
Download the Teams desktop app, run it, and sign in at least once.After signing into Teams, restart the app.Restart Outlook (after restarting Teams).Ensure that the add-in is installed and enabled. If after all that, you still don't see the add-in, make sure that it isn't disabled for some reason.
In Outlook, clickFileand thenOptions.Select theAdd-instab ofOutlook Optionsdialog boxConfirm thatMicrosoft Teams Meeting Add-in for Microsoft Officeis listed in theActive Application Add-in…