There was "Arch Linux ARM" ("ALARM") for a while but all updates that happen to it currently are automations. Stuff breaks more and more from time to time and the maintainer is unresponsive. I am assuming that's why the Asahi project moved to Fedora. And a new proposition inside of Arch Linux allows a "port" to be made but nobody submitted anything. It needs 2 maintainers minimum.

Anyways, so what I am assuming happened is that they just did their own port and never released the build scripts, because of course they would.

From what I've heard, only a small "base" is actually running natively and FEX has it's root set to a specific variant of the "Steam Linux Runtime" (you know, like when you install something on Steam it installs that?) fit to run Steam itself rather than games, but that's just my hypothesis.