I wish distros would not package pre-alpha software, since the only thing it accomplishes is giving people a bad first impression of something that isn't ready :(
If you want to mess with Ladybird, build it from the source at https://github.com/LadybirdBrowser/ladybird :)
Clearly, some upstreams do not appreciate that NixOS provides non-standard or sometimes-unfinished versions of their software, but it's either that or the software is essentially unusable and uncompilable on NixOS.
I do wonder if there is a potential for productive compromise, though. Maybe it would be desirable to have a QMessageBox warning to the user at startup that the distribution is unsupported and bugs should not be reported upstream. I think that the folks maintaining the Ladybird derivation would be happy to take feedback into account.
If that doesn't work, please open an issue in the nixpkgs bug tracker.
I'll check back every few months and see how it's going!