Hi @thijs p
Welcome to our forum!
It seems your case is more related to Microsoft Authentication, please kindly understand that the Outlook tag here we mainly focus on general issues about Outlook desktop client. It's suggested that you could post your case in dedicated tag for Microsoft Authenticator for more professional advice: Microsoft Authenticator - Microsoft Q&A.
In addition, you may reach out Customer service phone numbers - Microsoft Support to get some more direct assistance.
Thanks for your support and understanding.
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