The process to record a mixed reality video using an Iphone XS (or later) and a Quest2 headset.
You need to install the Reality Mixer app from the app store on your iPhone
You also need to install the MRC app onto your quest2 headset by opening your browser and going to https://www.oculus.com/experiences/qu... (you'll need to login using either your Facebook credentials or Oculus user credentials, whichever you use on your Quest 2).
Another useful tutorial can be found here • Tutorial: Mixed Reality with an iPhone and...