It's should appear at Xcode release note, but right now there's no the information about the RealityKit issue yet
chatdep
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If you need to finish the work right now, you can download the Xcode 13 beta 3 instead of waiting for the next release which may not be fixed in the next release :(
Xcode 13 beta 3 is still able to recognize the iOS 15 beta 4
No problem, If you need other versions, you can check all available right here
I've just tried it on Intel based Mac, then It looks like the freezing problem is on M1