Xcode downloaded from the App Store does not run on macOS 27 (beta 3). However, as you point out, I can drill down into the Xcode.app bundle and still open Reality Composer Pro 2 directly and create USDZ files on macOS 27.
For now, I have moved Xcode 26 (from the AppStore) to /Applications/Legacy/ on my macOS 27 Mac. I don't know how long this will work as a work-around.
Topic:
Spatial Computing
SubTopic:
Reality Composer Pro
Tags: