Additional sign-in or account-related issues within Microsoft Teams for business
I ran into this same issue and with a little digging I found this: https://support.microsoft.com/en-us/office/sign-up-and-create-a-teams-free-org-with-a-gmail-account-5e6db51b-1edf-400d-bf55-51366cf4384e
following the instructions here, I was able to create a new account online and then login through the application.
Hope this helps someone.