Turn off Phone Display when NReal is connected? (DEX?)

Is there a way to turn off the phone display when you are wearing the headset and are just mirroring the display - it seems very wasteful on the battery to have both displays running.
I have not seen any option in Android where this can be done with the exception of an app that needs a phone to be rooted in order to function. I have a Galaxy Z fold - the only way to get a full screen display it appears is to have the phone unfolded. It would be good to have some form of display management - being able to use DEX would also be an option - any chance of that being fixed?

On a factory reset Note 9 -the phone opens DEX and turns off the phone display correctly . My understanding is that the latest version of DEX “broke” this functionality -does the fix sit with Samsung or with Nreal?
Or is this " working as designed"
It would be nice to have the option to switch between DEX, Nebula & Casting

I asked Nreal; they will investigate it.