I am surprised you haven't proposed the most likely (and sadly boring) for me: 7) They are not aliens or any unexplainable phenomenon, witnesses are all delude

I am surprised you haven't proposed the most likely (and sadly boring) for me: 7) They are not aliens or any unexplainable phenomenon, witnesses are all deluded or victims of things like lens glare and the DoD has let them go public (importantly without stigmatising them) to: a) Encourage others serving at the frontline to come forward when they see UFO in case it is foreign adversarial tech (such as the spy balloon) without worrying of being stigmatised b) satisfy public demand by being as transparent as possible with the situation to prevent further delusion and conspiracy theories in the public.