Hello Timo,
Your account is probably trying to default login to the Azure Portal of a directory you no longer have access to.
Try pasting into your browser a direct link formatted as portal.azure.com/#@yourtenantdomain/
You can check with a coworker that has access what is the domain they get after login.
When you have access, check on your settings and define your default start up directory. Default is "last visited", and this causes issues when access is lost
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