Dear Philip von Gontard
I hope you're doing well.
I wanted to provide a quick update in case you haven't seen it yet. Another user, Frans Schlack, reported similar issue you've described, and it has been acknowledged internally. Microsoft is actively investigating this under Incident ID: INC6201353 – “Office 365 – Unable to Create, View, and Manage Contacts.” A resolution is in progress.
If you're a Microsoft 365 admin, I recommend submitting a support request through the Microsoft 365 Admin Center. This ensures your experience is captured and may help expedite resolution by associating it with the existing incident.
If you’re unsure how to raise a ticket, this Microsoft Community article provides a helpful step-by-step guide.
Thank you for your patience, and please don’t hesitate to keep us posted, we’re here to help and will continue sharing updates as we receive them.
I’d be grateful if you could mark my initial answer as Accepted. It helps others find this thread more easily and acknowledges the support you received.