I think there UAPs are either * Atmospheric effects * Debris from space launches, or other kind of debris in the atmosphere * Artefacts in optics/radars * H

I think there UAPs are either * Atmospheric effects * Debris from space launches, or other kind of debris in the atmosphere * Artefacts in optics/radars * Human illusions * Secret flying devices from various countries * Aliens I think the top 4-5 possibilities are very likely. Realistically there are a plenty of cases where it's impossible to refute more interesting hypotheses, but since they are much less likely and there is no strong direct evidence for them, I personally don't consider those too seriously.