You can now root all Meta glasses https://github.com/Lumince/singularity/releases/

You can also, without root, use Termux letting you install a local server on the device itself, use adb to start the browser on a WebXR page running on it, etc.

So it's possible to make it work and entirely offline, no Meta account, no app, all this without privacy concerns but that does require to tinker a bit.

I document this a bit on https://git.benetou.fr/utopiah/biggu_s_gate/issues/152 so feel free to ask more questions