Hello @Jan Moeyaert ,
Thank you for posting in the Microsoft community.
I understand the issues you're facing with the Microsoft Authenticator app.
If your account is Microsoft365 Work/School account and if you are an end user or if you are admin but other user has admin rights, please contact your admin to reset your authentication method. They can do this by following the "Manage user authentication options" guide. If you're unsure who your admin is, refer to this article: How do I find my Microsoft 365 admin?.
Your admin will implement the steps outlined in the article to help you reset your authentication method. Once this is done, you should be able to receive the approval codes on your phone and regain access to your account. Manage authentication methods for Microsoft Entra multifactor authentication - Microsoft Entra ID | Microsoft Learn.
However, if you're the sole admin in your organization, we recommend contacting our dedicated data protection support team directly for assistance. You can find the support phone numbers by country or region here: https://learn.microsoft.com/en-us/microsoft-365/admin/support-contact-info?view=o365-worldwide .
Let me know if you have any more questions in the comments.
I hope this information is helpful. Please feel free to reach out if you have any further questions. If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Thanks,
Chaithra.