I just got the nreal air recently. Don't know if the nreal light is the same but the airs can be just used as a display through dp alt without the app. However, instead of a floating screen in a fixed position, it will just be a static display that moves with your head.

I will also say, for the nreal airs, they're not quite there yet. It's blurry throughout and completely unreadable off center, I find myself moving the glasses around so different parts of the screen will be in the center. Regardless of center or edge they they're always a bit blurry and hurt my eyes, and after taking them off I can't focus my eyes on things far away. I still like them as a low resolution screen for watching youtube while washing the dishes for example, but their use is quite limited.

I don't think you can, but activation is pretty straightforward through either a phone or a pc with usb c with display port alt mode.

Yes, Nreal Air (March 2023) without activation.