Help - Cannot log into Teams account via Win10 app

I wonder if anybody here can help me?

I have a free Teams account and have set myself up as administrator of my own organisation.

I can log in fine through my Chrome browser......and do everything I need - though the web interface is limited.

I have the Teams app installed in my desktop machine - but this refuses to log into that account.

When I try to log in it just says  "We're switching you to your other account. It'll just take a moment...".

It takes a couple of minutes then takes me back to the login page.

I have tried uninstalling and reinstalling the app.

I have tried deleting the contents of appdata\Microsoft\Teams

...but no joy.

It's entirely illogical....I think. Any help gratefully received.