Flathub is only okay with NixOS because a lot of flatpaks escape their sandbox and call out to outside programs. Sometimes you need to compile a NixOS version since the paths are not the same as a generic Linux distro. I've asked the developers to take a look at it, and one of them closed the issue, and the other is going to try to make it work with steam run
Basically, nixpkgs is still the best way to run something on NixOS
Basically, nixpkgs is still the best way to run something on NixOS