It's should appear at Xcode release note, but right now there's no the information about the RealityKit issue yet

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