Microsoft is resolving a known issue that causes "couldn't connect" errors when launching the Microsoft Teams desktop and web ...

Delete all the sub-folders and files in that folder. Finally, restart Microsoft Teams and see if the issue is fixed. NOTE: Clearing Teams cache will not make you lose any user data.

Since it is a login error, the first thing need to do is to delete the Microsoft Teams Credentials and retry logging in. To clear the credentials, you can follow the given steps.