Some W3C services might not correspond 1:1 to public repositories, and some might be obscurely named. A place to recommend untriaged bugs be reported to for transfer (which GitHub supports) would be an improvement. Otherwise, I would report them to .github/issues by default.

Some examples of when this would be of use are:

1. ...when reporting bugs to Tracker (like WAI/APA/track/users/?login): ¹

   Tracker's code (which resides in WWW/2005/06/tracker/src) hasn't been released at this stage, as it relies on the specific schemas of W3C internal databases.

2. When reporting documentation problems, like w3c/process/issues/130#issuecomment-3349176507 describes. An example of one of these is /html/body/p[9] of w3.org/2019/01/bugzilla-shutdown.html#migration)'s placeholder:

   (this section still needs work)

Obviously, no correspondent repositories, nor Bugzilla products, exist for those. ²