> It's a special version of Android that has a developer mode that unlocks a virtual (sandboxed) Linux environment

Android for mobile (at least on Pixel phones) has this too.

The "special" bit is the desktop experience. New Pixels have a desktop mode if you plug them into a monitor but it's not as fleshed out and doesn't have their Gemini-ified cursor etc. At least not yet.

I think your notes re. ARM and Qualcomm hit the nail on the head though!