Microsoft has finally answered the user. In particular consultants who not only advise one customer, who "fought" in the past repeatedly with sign in dialogs to Office 365, Office Online or OneDrive for Business.
So it could well happen that you started your PC and after logging in and starting the process another user logon dialog has been cast on the screen, you may sign up.
All users who call only one tenant his own, have had no problems which data to be entered.
But the people who have to work with more than one tenant, have had a hard time.
What data are to be entered?
Today I noticed the first time, but now the dialog display the tenant name.
For Microsoft, a small step, but for the users the try and error process has an end.
Thank you Microsoft.