The obvious answer (and I’m not trying to be flippant here) is that someone once added a tag for Nobara.
In this forum we provide help and support for all the Fedora spins. Including the atomic versions.
However, if it’s not a Fedora spin, then we have no idea what has been done to it to make it significantly different. We don’t offer support for Nobara in the same same way that we can’t and don’t offer support for CachyOS or any other derivation of a Fedora release or spin.
To add to the comment by Steve above.
On the opening page when going to the Nobara site there exists a description of the many changes from Fedora. It shows that Nobara is significantly different than Fedora and thus we cannot support it.