The metal support for pytorch is a real sh*t show at this point - all APIs are either legacy or unfinished. Also, app memory is about 3GB even for the largest phones.
It really still feels that it‘s all in its infancies.
PyTorch came from PCs running on GPUs with their own pool of dedicated memory and a slower link to main memory.
I know people have been speeding it up a lot on Apple processors, but I’m not sure it’s a good indicator of how ready the iPhone is for running models for end user programs.