IIRC AVPlayerViewController has the same limitation -- it can show 3D if it's in its own window, but falls back to 2D if embedded in a SwiftUI windows. It sounds like the OS might be rendering UI to a monocular target, so your best bet might be rendering to a stereo render target, and displaying it on a RealityKit quad with a custom RK shader for showing the correct image on each eye.
GiantSox
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