Sorry for the confusion here. The good news is Portal plays both Static (Fixed) Spatial Audio as well as Dynamic (head tracked) Spatial Audio, however unfortunately the Control Center doesn’t recognise that it is.
The reason for this is Dolby Atmos is the default spatial audio format that Apple uses and while it is well suited for music and film, creating a reverb that's conducive to making you feel as though you're in a music studio or a cinema, we found it didn’t work so well for our specific goal of recreating natural outdoor ambient experiences, where sound is expansive and dynamic. And so instead of using Dolby Atmos, we partnered with Atmoky, a world-leading Spatial Audio R&D company, to deploy a custom spatial audio format which uses higher order Ambisonics (often used for VR) that are better suited for faithfully recreating the auditory experience of actually being in nature.
With Atmoky's assistance, the Portal app renders the spatial audio itself, and therefore by-passes Dolby Atmos entirely. As a result, the Control Center does not recognise that spatial audio is being played and will therefore indicate that Spatial Audio is “Not Available”.