To reiterate, I’m not seeking help to install the package, I’m just trying to understand the error message which, to me, makes no sense.
The -bb option indeed seemed to give a more meaningful response, and my deeper dive into rpmbuild seems to suggest that the -tb option is basically deprecated everywhere, so maybe I shouldn’t be surprised that it came back with nonsense, so I’m gonna walk away from this rabbit hole!
That said, you mention ‘modifying the spec to use [OM] requirements’, but I can’t find where those requirements are described. The best I found was this page, but it doesn’t really say anything specific.