I've had better luck exporting from Blender to USD or USDC and then loading that into Xcode. AFAIK, there is no blendshape support in RealityKit, You may want to try something joint based.
https://developer.apple.com/documentation/realitykit/validating-usd-files?changes=_3 < feature support comparison
Good news - RealityKit has advanced spatial audio support (and support for embedded audio. Good luck!
ForestAR
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I split the animation files into individuals, zip them and then apply files from the zip archive as needed.
This version of USD Python tools uses Python 3.7. You can download and install Python 3.7.9 (recommended) from
usdzconvert (version 0.66)
https://www.icloud.com/iclouddrive/0c3_rLAbsLWM5JHOU_CfgubZA#chibi%5Fgenesis2.gltf. <<< Example file
Reality Converter vs 1.0 (53)
The smallest I can get the USDZ file output is from RealityKit @ 1.5mb. Other methods output 4mb+, including USDZ tools and Blender 3.5. I imagine Reality Kit is performing some automated optimizations, but it would be nice to know what they are, and how to get these smaller sizes from the command line.