The hardware itself is utilized by many pieces of software on any Apple device. Face ID uses it, Siri uses it, the camera uses it, there are also other Apple on device LLM features, where you could easily test whether the basic capabilities are there.
I highly doubt that you could have a usable iPhone with a broken neural engine, at the very least it would be obvious to the user that there is something very wrong going on.
I highly doubt that you could have a usable iPhone with a broken neural engine, at the very least it would be obvious to the user that there is something very wrong going on.