PT3 · S4 · Q18 Physicalists” expect that ultimately all

This describes the famous Self Contradiction flaw, which we know is almost never a correct answer. The conclusion is very compatible with the claim by the physicalists. Both claims are very optimistic about the idea that mental functions will be explainable in neurobiological terms.

Flaw answers that complain that we don't know specific numbers / names of sources / specific details are almost always wrong. In terms of reasoning, if I tell you that "Doing X requires A, B, and C", it's okay for me to state premises that "A and C have been achieved" without providing all the details and backstory on how they were achieved. Even if the author were to have included ten pages of information about the basic functions of neurons, we'd be no closer to judging the conclusion. We still wouldn't know: a) where are we at in terms of knowing how neurons interact b) are there any other requirements for achieving this goal besides the three that were stated

These words weren't used interchangeably. We don't really get any definition of mental function but presumably we're referring to mental processes like "doing multiplication" / "remembering a quote you once heard", etc. A neurobiological explanation would describe that mental activity in terms of the various neurons and brain parts involved. At no point is the author treating these equivalently.

Sure, the author doesn't indicate whether this ability will be useful in any way, but they don't need to. Their conclusion is only trying to prove that a neurobiological explanation will be possible, not useful / good.