Processus dans Microsoft 365 pour configurer des applications Office, entrer des clés de produit et activer des licences.
Dear Estelle DELTOUR,
Good day! Thank you for posting to Microsoft Community. I am happy to help you.
From your description, I understand that you can't share some files in Teams and when you and others plan, you can't assign tasks even if you assign administrator rights.
In my experience, both of these issues may be related to the server's failure to recognize the user properly. To help you fix this issue, you need to contact Microsoft Support and ask them to help you see if there is a problem with the server. I also appreciate your understanding that as a forum moderator I do not have access to background data.
In this situation, I am sorry and recommend you to connect with the related development team where they can check the internal sources and investigate the issue further.
So, I request you to connect with your IT admin of your organization (How do I find my Microsoft 365 admin? - Microsoft Support) and ask them to raise a new service request from the Microsoft 365 admin center so that the related development team will connect with you and investigate the issue further.
Reference: Get support - Microsoft 365 admin | Microsoft Learn
Note: I apologize for redirecting you to related development support team because the moderators in this community are limited with the resource for further investigation and to get a quick resolution to your problem, I requested it.
Thanks for your cooperation.
Have a good day!
Sincerely,
Tin | Microsoft Community Moderator