So, wtf is Onyx and how does it violate GPLv2?
So, it doesn't need to be publicly available (as in, you and me are not Onyx users, therefore we don't need to have access to it), just to its users. Screenshot shows their user requesting it and being denied the request, hence, GPL violation.
https://www.gnu.org/licenses/gpl-faq.en.html#GPLRequireSourc...
_and distribute it_
Running it server-side is fine. That's what the AGPL addresses.
If you modify GPL code and only use it yourself without distributing it, you never have to give anyone else access to the modifications.