I believe that angels are the constructs of God. Beyond that - ascribing alien spaceman qualities or UFO greys eating human remains in slurries e.g. - I do not go.
I haven’t seen anything in the description of an ET which would preclude the soulish identification of some angels by unbelievers as an “ET”.
The possibility of something does not prove that that something exists.
I have no doubt both exist, though I am not prescribing more than what is presented inn either Scripture, or by experience in the physical or spiritual domain.
I have read some ‘secular’ reports regarding human remains in slurries, but I am no going there, nor have supported nor denied such in this discussion.
FWIW, the ability of man to prove or disprove the existence of angels will never influence their existence. any more than man being able to prove or disprove the existence of God. Their existence is not dependent upon our cognizance or ignorance of them.