https://developer.apple.com/arkit/gallery/ - pretty link to models for augmented reality in Apple's use of Pixar's usdz file format. The tools link on that page leads to .zip that unpacks to a directory of samples and a python script that wraps a Mac compiled binary from
http://openusd.org the public USD Github repository. A usdz file is a zip of a .usdc file and its assets.
neural engine - This looks like its a marketing term. A search of Apple's programmer documentation turns up:
That is, layered neural networks implemented as shader code running in Metal.
The best discussion I've found on ARM 8.3 pointer authentication: the compiler generates function prologs so when a function is called normally the return address on the stack gets mangled with encryption, and the function's return instruction is a new opcode that validates the encryption before returning. If an attacker crafts a pointer to jump into the middle of a function, then the RETA will try to decrypt, fail, and crash the app.