Changing between multiple Teams Free accounts within the app or browser
Not quite sure I understood the question. Although maybe the problem has been solved.
Went into my account list. "Signed out" just below the list. (I had always "exited" with the exit button in the upper right hand corner before.) Started Teams again and this time the "Office" account came up without having to select it from the list of accounts.
So...it seems to be working now. Will keep you posted if it acts up again.