I would also like to know how to test SharePlay on the Vision Pro. Even if I had two headsets, which I don't, I can only wear one at a time. I think Apple needs a solution for this if they expect us to implement Shareplay at all for this platform.

Yes! Wrapping my attachments in Attachment(id:){} worked. I would have never guessed this would have been the solution with that terrible error message so thanks for your help.

Same issue. Compiling against anything RealityKit is not working