I've always felt that the different aspects of the mind have been very loosely defined. We've lacked the science to really define them specifically. ("What is consciousness?" remains a philosophical question, which is a strong queue that we don't understand the science of the question yet) And until recently, we've lacked a lot of basis for comparison. (animal intelligence and consciousness _should_ have been a basis for comparison, but I think for cultural reasons we've been quite late to make peace with that fact.)

In any case, intelligence, consciousness, sapience, ego, etc. will probably need more strict fact-based definitions before we can agree on whether or not artificial consciousness can exist.

My personal theory is that consciousness is a specific biological adaptation, and it exists primarily to manage the care of young, and to manage status & relationships in kin groups. A theory of mind can benefit the care of young, which is a good argument for why it appears that only mammals and birds (two classes of animals which do a lot of caring for young) appear to either have a prefrontal cortex (mammals) or appear to have developed something which performs the same functions. (birds) In my opinion, consciousness as people experience it is also necessary for developing a theory of mind for other people, which is beneficial with regard to understand status & hierarchy in a group, and for cultivating and maintaining status.

This is partially why you can be a mystery to yourself; the same skills you'd use to try to understand someone else must actually be used to understand yourself. eg: "was I secretly jealous when I cut down my coworker?" Why don't you just know with 100% certainty? I'd argue that it's because the maintenance of ego does not require this certainty, because ego is tacked onto an already developed brain and lacks perfect insight into the brain's processes. I'd also argue this is why there can be such a gap between who someone believes themselves to be, and who they actually are. You're maintaining a personal identity which ties directly to status. It's not super relevant whether you're consistent over time or 100% internally consistent. You must meet the threshold to maintain your status, but really no more is needed.

It's also why you talk yourself in inane ways. You're walking through your house and you finally found your lost car keys. "I found them!" you might say to yourself. But who are you telling? Certainly "you" already know. I'd argue that the "you" in your head is an abstract identity that you have imperfect access to -- just the same as you have imperfect access and knowledge to other people. Your mind builds a model of your own mind using the same tools it uses to build a model of other people's minds. You have _more_ information about your own mind, but you certainly do not have omniscience about your own mind. The models are always imperfect.

I could go on, but I'd also argue this is sort of the basis for religion. Just like we see faces in the clouds, we try to find a theory of mind in places where it doesn't actually exist. (eg: "We must have upset an ego out there, and that's why it's not raining.") I also think it's why people have moral intuitions but not mathematical intuitions. Or why moral intuitions fail at scale. (eg: Peter Singer's famous child drowning in a small pond thought experiment.)