Hi Jens,
Are any of your users Global Administrator in your Entra ID tenant? If yes, please follow instructions in article below to elevate access:
Elevate access for a Global Administrator
Once the user has elevated access, sign out and sign-in again for the change to take effect.
Next navigate to subscription in Azure portal, then on left click Access control (IAM) blade.
Click Add -- Add role assignment, next click Privileged administrator roles tab, select Owner, click Next, click Select members, search for and Select your account, click Next, on Conditions tab select Allow user to assign all roles (highly privileged), click Review + assign, Review + assign.
After you are finished please remember to toggle the elevated access back to off.
Please reply back with your results, whether positive or negative. If you have any questions please add a comment below.
Thanks.
-TP