Just for the inspiration to solve the problem in your case.
I managed to scope down to the root cause of my problem which come from one .usda file in my RealityKitContent Package. Inside that there's a quite ShaderGraphMaterial that has some internal part references back to another .usda file that I didn't copy to the new RC Pro project. Also has modules from older version of RC Pro. I guess the compiler fail to compile this and cause the error (for my case).
As long as my RealityKitContent doesn't use this file it's going on well. (the moving Xcode to another folder, clear DerivedData folder, restart Xcode & Computer, etc. sometimes solve the problem but it reappears. Only this way effectively persists)
pichaya_TRYYS
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This happened to me, too. I tried so many ways. Last thing that solved the problem was moving newly downloaded Xcode which I expanded in Downloads folder to "Applications" Folder and it just worked (after the Xcode restarted).