You are aware that you are trying GUIX out on hardware which has been tightly locked away from being interoperable with anything besides MacOS, right?
When there's a limited scope of what drivers are required, it should be easier, not harder, to support certain hardware. Being unable to read NVME drives (which have been around since 2011) is no longer acceptable for an OS in 2020.
Maybe I'll try it again in a while. Not sure if it's available for raspberry pi, but it would be great to try it there and eventually switch to it on my laptop (once JJ change WiFi card!)
Guix rejects non-free software in their repos, so I would be unsurprised to hear that no contributors use Apple hardware.
I agree that what you are trying to accomplish should be doable and even non-trivial. This is definitely a disadvantage of having a more automated installation procedure.