Hi @D. de Jong
To narrow down this issue, I would like to first confirm with you:
Are you using a personal account (for example, you are logging Teams with your Gmail account) or an account managed by an organization (if yes is it your home organization or another organization)?
From your description it seems your account is managed by your organization.
Please have a check if it is the same behavior on Teams on the web.
If the issue persists, please post a screenshot of this issue.
(Don't forget to hide your personal information in it)
If possible please also contact your tenant admin to check your account status. (is it a still normal user account or it was changed to a guest account or other changes have been done before the issue occurred).
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.