Using Classic Outlook on Windows for personal email, calendar, and contact management
Exact same thing I'm seeing here unfortunately, although speaking to other colleagues on the same build version they don't have this new report button, so doesn't seem like it on everyone's outlook.
I think if it becomes more of a problem we will just have to advise users to either remove it from their ribbon manually, or advise them to ignore and use the third-party one all the time.