I won't disagree that guix can be made to use nonfree packages. However, the claim:
>> Although if you look at FSFs major projects Emacs and gcc they do run on many OSs including non-free (e.g. Solaris, macOS, Windows, VMS and virtually anything that exists) and other free Unixes.
>> GUIX is much much more restricted.
appears to hold up; https://guix.gnu.org/en/download/ says "Alternately, GNU Guix can be installed as an additional package manager on top of an installed Linux-based system." (emphasis mine) and although there's no explicit statement, https://guix.gnu.org/manual/en/html_node/Installation.html implicitly reiterates that guix is only targeting Linux. Forget running on Solaris, Darwin, or NT; as far as I can tell guix doesn't even care about being usable on any open source unix other than Linux.
Edit: Although now that I think about it, they also target HURD... which is no less niche, but does at least imply that it could work on non-Linux unixen.
>> Although if you look at FSFs major projects Emacs and gcc they do run on many OSs including non-free (e.g. Solaris, macOS, Windows, VMS and virtually anything that exists) and other free Unixes.
>> GUIX is much much more restricted.
appears to hold up; https://guix.gnu.org/en/download/ says "Alternately, GNU Guix can be installed as an additional package manager on top of an installed Linux-based system." (emphasis mine) and although there's no explicit statement, https://guix.gnu.org/manual/en/html_node/Installation.html implicitly reiterates that guix is only targeting Linux. Forget running on Solaris, Darwin, or NT; as far as I can tell guix doesn't even care about being usable on any open source unix other than Linux.
Edit: Although now that I think about it, they also target HURD... which is no less niche, but does at least imply that it could work on non-Linux unixen.