Hi @J-3804
To troubleshoot the issue of Microsoft Teams add-ins in outlook client, you could try to refer to this document's steps to check if it works for you.
In addition, please make sure you are using modern authentication to sign in Teams and enable private meeting, or you cannot make add-in to get deployed.
If the above suggestion is not work for you, could you tell some answers of your situation:
1) Do you mean you met the same error messages like the link you provided?
2) Can you use Teams meeting in outlook web client?
If the response is helpful, please click "Accept Answer" and upvote it.
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.