According to 'Prepare to deploy add-ins in Integrated apps', if you distribute your add-in to users in your organization by using the Microsoft 365 admin center through Integrated Apps, the add-ins are supported on Mac.
As this issue is related to Microsoft 365 Admin Center, it's recommended to post a new thread on Microsoft Tech Community --- Microsoft 365 admin center.
Thanks for your understanding.
Following information is my personally opinion.
- Remove 3rd-party add-ins from Office for Mac if there is.
- How did you reinstall Office for Mac, I suggest you download the installation file from this link: https://learn.microsoft.com/en-us/officeupdates/update-history-office-for-mac#release-history-for-office-for-mac
- Make sure that the account you are currently using is the licensed account.
- Create a new user account on Mac for a test.
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