Adjusting alert preferences for messages, mentions, and activity within Microsoft Teams
Thanks for your information.
I was able to reproduce a similar scenario in my testing.
In my test, when Microsoft Teams was used with a non-Microsoft email address (Gmail), Teams created a Microsoft identity in the background and meeting responses were routed to a Microsoft-generated Outlook address. That explains the Outlook.com account with random user name behavior.
When attendees accepted the invitation, the acceptance response was sent to that Outlook address rather than directly to the Gmail mailbox.
In my testing, the attendees were still able to join the meeting successfully by using the Teams meeting link directly. The issue only affected the meeting acceptance response. Based on my testing, this behavior appears to be related to using a non-Microsoft email address with Teams rather than the use of a Mac device.
Therefore, my current understanding is that the rejection message is occurring because the meeting response is being routed to a Microsoft-generated Outlook address associated with the Teams account, while the primary account itself is a Gmail account. As a result, the acceptance email cannot be processed correctly, even though the Teams meeting remains accessible through the meeting link.
In summary, this does not appear to be a macOS issue. The behavior seems to be related to the account being configured with a non-Microsoft email address rather than a Microsoft 365 or Exchange Online mailbox. I'd recommend you to give the direct Teams meeting link. Or if your prefer scheduling meeting via email, setting up a Microsoft account is an alternative approach. (personal or business account depends on your need)
I hope this explains your concern.