The link to download “MaterialX definitions” is broken on the main page of ShaderGraph documentation in the Interoperability section. See here: https://developer.apple.com/documentation/ShaderGraph#Interoperability
Link in the page is https://developer.apple.com/augmented-reality/realitykit/files/MaterialX-definitions.zip but leads nowhere now.
Since Reality Composer Pro 3 has been released, it would be good to have these definitions available to download again and to know if it’s still MaterialX 1.38 being used in the updated RCP & RealityKit.
Opened a ticket about this: FB23258836