Welcome to our forum!
Please kindly understand that the Outlook tag here we mainly focus on general issues about Outlook desktop client. Looks like the issue is more related to Graph API, which we are not very familiar. The following is for informational purposes only.
Based on my search, the reasons for the error code AADSTS1002012 could be:
The provided value for scope {scope} is not valid. Client credential flows must have a scope value with /.default suffixed to the resource identifier (application ID URI).
Also, I found a similar thread, you can refer to: https://stackoverflow.com/questions/73210134/microsoft-graph-authentication-problem-when-switching-to-client-secret-the-scop.
Hope this helps!
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.