What if the more difficult to explain parts of the UAP phenomenon is our experience of the remnant of that previous civilization? It never went extinct, it just

What if the more difficult to explain parts of the UAP phenomenon is our experience of the remnant of that previous civilization? It never went extinct, it just moved into space and the bottom of the oceans. We're ants, unaware of the civilization that surrounds us because it is to alien/advanced for us to comprehend.