> Consciousness is an illusion
It's just like the related "Free will is an illusion".
With "illusion" just referring to something that appears to be one thing, when it is in fact something else.
In the case of free will - we all feel as if we have it, that our future actions are under "our" control, but if we assume or brains and muscles are subject to the laws of physics then this can't be correct. We're just a meat machine. We can watch the decision making in progress and easily believe that some mysterious actor "me" is the one doing it, but in reality the meat machine is doing everything, including the self-observation, and the sense of self is just as illusory/misleading as the sense of free will.
Consciousness, rather closely connected to sense of self, can be described as illusory since it makes us feel that "being" or "experiencing" are something fundamental, some aspect of being "alive" that is distinct from the computational machinery of our brain that is otherwise doing all the perception, cognition, emoting, etc. But, again, the meat machine argument tells us this must be wrong, so it's reasonable to call consciousness an illusion - not what it seems to be, even if there is some real self-observational computation behind it ... it does exist, but it's not magic.
A useful thought experiment for anyone who believes that a sufficiently brain-like machine wouldn't experience qualia - e.g. the feeling of seeing something - is to try to pinpoint exactly what aspect of the feeling the machine would be missing? The expansive sense of color/vision as a spatial quality perhaps? The grass-like freshness of new leaves on a tree blowing in the breeze, perhaps? ...