Simpler than that, you can just talk to the cryptography IC yourself and ask it to sign stuff. No need for an FPGA, just an arduino. Given the datasheet I imagine any LLM from the last year should be able to oneshot it.
I imagine on apple silicon this is buried deep in silicon / ISP IP block, and isn't a discrete IC.
You're talking about the device that's in the blog post; the person you're replying to is talking about the thing that Apple is shipping soon.