Based on your case description, it is recommended that you sign in to the Microsoft Entra Management Center using one of the following identities: Cloud Application Administrator, Application Administrator, or owner of the service principal.
Then browse to Identity > Applications > Enterprise applications > All applications.
Search for Microsoft Teams Web Client > then select Properties.
Please select Yes for Enabled for users to sign-in? and save.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.