Ants live in cities surrounded by humans, but have no idea what a human is or what humans do, and literally cannot experience - never mind imagine - what a human is, what a city is, what transport networks are, what culture is, what technology is.
Every so often an ant nest is destroyed because it's an irritant, but if the ants notice at all they carry on relatively unthinkingly. There are only other ants, pheromone trails, and food sources. [Other] may register very fleetingly but does not align with any ant concepts or ant goals, and therefore leaves no lasting impression.
Wide differences in intelligence make more advanced lifeforms invisible - not physically but conceptually. Which turns out to amount to the same thing in practice. Even between two species who share the same physical space.
We could be surrounded by a universal or galactic civilisation and we wouldn't know.