There is probably an obvious answer to this, but better ask lest I do something wrong. I just came across a broken package (mermaid-cli), apparently some dependencies are not getting installed.
In the search page there is an e-mail address. I would rather not contact someone directly and instead have an (open) recorded report. I could possibly open an issue at the NixOS repository, but there are currently over 5 000 issues open there. Feels like sending an issue to a black hole.
That is to say, it’s alright to open an issue as long as you ping maintainers, otherwise it likely won’t be found by anyone. Ideally though you would open a pull request with the fix!
And there are 31,000 closed ones, it’s a decently high-traffic repo with 10+ years of history.
Also, 2000 of those issues are “packaging requests” i.e. requests for new packages, now that is a black hole. But actual bugs tend to get looked at when tagged appropriately.