I face the same issue: Can't import RealityKit on Xcode Version 13.0 beta 4 (13A5201i)
When I went back to the beta 3,
Make sure I'm opening the Xcode 13 Beta 3
Clean the build folder by shift + cmd + k or Product/Clean Build Folder
(Optional) Delete the contents in /Users/YOURCOMPUSER/Library/Developer/Xcode/DerivedData
Then, I can compile the app with Xcode 13 Beta 3 again
Hope this help
chatdep
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