I checked the repo but there's no code? Just some HTML etc.
It seems like they just plan for this thing to exist but it doesn't actually exist yet?

EDIT: Their explanation:

This repository is currently in its early setup phase.

At the moment, the repository mainly contains project scaffolding, policy files, and the initial project direction. Firmware sources, board support, build instructions, and flashing guidance are still being prepared.

That means zgm is early, but it is intentionally early in public. The goal is not to wait until everything is finished before opening the door. The goal is to make the long-term direction visible and let the project grow into a useful open firmware platform in the open.

I'm not sure if that means that they still have to make it, or that they just have to finish it before publishing it?