For most applications, we don’t want “functionally identical”. We do not want it to have its own desires and a will of its own, biological(-analogous) needs, having a circadian rhythm, getting tired and needing sleep, being subject to mood changes and emotional swings, feeling pain, having a sexual drive, needing recognition and validation, and so on. So we don’t want to copy the neural and bodily correlates that give rise to those phenomena, which arguably are not essential to how the human brain manages to have the intelligence it has. That is likely to drastically change the ethics of it. We will have to learn more about how those things work in the brain to avoid the undesirables.