Unfortunately it doesn't - even if our package definition doesn’t change output may, since software referenced by the package’s build function is not bit by bit reproducible.

The biggest issue is with Linux Kernel itself. Once kernel reproducibility will be handled, we can practically claim Guix, NixOS, Debian or any other Linux distro is reproducible as well, since with little effort we can avoid installing packages which will colour our reproducibility.

For desktop environments it’s a bit worse, but there are huge efforts to make this happen for all packages in package registries of aforementioned distros.