I'm building a SwiftUI+RealityKit app for visionOS, macOS and iOS. The main UI is a diorama-like 3D scene which is shown in orthographic projection on macOS and as a regular volume on visionOS, with some SwiftUI buttons, labels and controls above and below the RealityView.
Now I want to add UI that is positioned relative to some 3D elements in the RealityView, such as a billboarded name label over characters with a "show details" button and such.
However, it seems the whole RealityView Attachments API is visionOS only? The types don't even exist on macOS. Why is it visionOS only? And how would I overlay SwiftUI elements over a RealityView using SwiftUI code on macOS if not with attachments?