I appreciate that the Surface Duo isn’t currently on the supported devices list, but I thought I’d share some of my findings, because I’ve seen a few people mentioning trying to use the Nreal Air with a Duo.
I’ll start with the main point:
MR Space, does not work 
As others have mentioned, when going into MR space the sound plays for the start up animation, but there is no output to the screen. Waving the phone around, you can hear the sound of the pointer going over the buttons in the MR space, but there is nothing on the screen.
After playing around for a bit I realized that it was actually possible to see the MR space by folding the phone from dual screen mode, to single screen mode (folding it back to back).
This appears to cause a full screen refresh and causes the MR space to render a single frame. So now I can see the MR space, but it is frozen on a single frame which still isn’t very useful.
It seems that the MR space is rendering but the screen isn’t updating (or something like that, I’m not an android expert)
Following along with this idea, I was playing with the android developer options for a way to force the display to refresh, and found that by enabling the “Show surface updates” option, the screen is forced to refresh on every frame…
Success! I can see the MR space in front of me, it tracks properly with my head movements, I can use the phone as a pointer and i can open apps!
Only one slight problem… The “Show surface updates” option will cause the screen to flash purple for a frame wherever it is updated, and because the whole screen is being updated, what you actually get is a headache inducing strobe effect as every other frame the screen flashes purple 
so, although it is possible to use, it isn’t really usable.
Another point of note: When in MR space, if you fold the device back into single screen mode, the MR space will only display through a single eye 
Anyway, that is my exploration so far with the Nreal Air and Surface Duo. If there’s anything I can do to help speed up getting the Surface Duo working, let me know. I have got the debug logs from my phone of plugging in the Air and loading the MR space on the Duo if that would be helpful to debug some of the issues?
I should also mention that I am using the apk from this thread Nebula APP for Non-GP Developers!
Thanks,
Martin