Intelligence is an interface-behavior not explained by physics. Consciousness cannot be an illusion, because having an illusion requires consciousness.
Please define "intelligence" and "consciousness" in the context of the observable universe. The only way I can see "intelligence" is to see an organism engage in complex problem-solving behavior, and the only way I can see "consciousness" is to see an organism respond to stimuli. Both of these are accounted for quite well by physicalism.
You basically claim that no observations can be made if an interface is present and all observations have to go though it.
I didn't say anything about an "interface".
I'll try to state it another way: I (using the word "I" for linguistic convenience and declining to open up a can of worms about the "self" at this time...) observe a physical, objective, world. For the sake of getting shit done, I assume such a world exists, that I'm not a brain in a vat or a butterfly dreaming I'm a man or the like, and that such world more-or-less corresponds to my observations; but we should not that this is an axiom and not a conclusion.
Phenomenon in this world, including the fascinating behavior of a certain ape species, seem to occur in patterns we can call "supervenience" and/or "reductionism" (where the same phenomenon can be looked at at different depths), and "causality" (where phenomenon follow each other in time sequence). It seems they could all in principle be explained as the complex dance of particles and fields acting over time.
I also observe a mental, subjective, internal world. Or perhaps it would be more accurate to say in the act of perceiving the external world and in perceiving memories, the existence of perception is implied.
This perception is part of the given, and it is singular and indivisible -- atomic, in a word. (In the philosophical sense, not the chemical sense!) As it cannot be divided, trying to investigate it by reductionist means goes nowhere. As it is singular and there are no other objects of its type to interact with it, causality is meaningless. This perception "just is". I perceive (or at least, something perceives, darn the metaphysical assumption coded into our grammatical conventions!) therefore perception exists. Perception is not part of the external, observable world, and so seeking some explanation for it out there is not meaningful.
Is there perception that is similar to but divided from that which is given as "my" experience? The question has no possible answer. If there was such perception, by its nature I would be unable to know it, since it is divided from the perception that I have (or that is "me", if you like).
Sure, as a practical and ethical matter, I make the assumption that there is such perception and that it is associated with at least some of the humans and other organisms I see "out there". It seems a bad thing when suffering comes into "my" perception and a good thing when pleasure comes into it; if there might be other perceptions it would be consistent to regard the suffering that comes into them as bad. Not knowing, I adopt a precautionary attitude.
But fundamentally, it's unknowable and unobservable. And trying to create an explanation within observable reality for something that can never be observed is inherently a fallacy, a metaphysical confusion.