I suggest grabbing a random DSLR with decent glass and trying to capture a bird in flight against the sky. Most of the time not even the species will be discernable. People with no prior experience photographing birds will have a hard time taking anything that is not blurry. It is actually not that easy even tracking something in flight through the viewfinder, especially at long focal lengths. Shaking, focus / depth of field, dynamic range, sensor noise and exposure time all work against you.
So I would be extremely suspicious of sharp clear properly exposed pictures of UFOs.
Birds are much harder to take pictures of than a UFO would, though. They are flying only a few meters above you, therefore having much higher and less predictable angular velocity, as well as requiring more lens movement to focus compared to infinity.
I can take clear pictures of airplanes flying ~400m above me without any issues.
I shoot birds in flight as a hobby. It takes some skill, but it's not _that_ hard. And a bird taking up 1/4 of your FOV is close enough that you have to focus on it. A plane/UFO taking up 1/4 of your FOV is much further away, and you can just pre-set your focus at 'infinity'. >1% of UFO photos should definitely be taken with good equipment by someone who knows how to use it.
I'm not the GP however I do the same, and even as a fairly lousy photographer I'm able to get photos where you can usually see some reasonable detail. Here are some examples: https://imgur.com/a/Nr5NIgt
All shot on a Canon 1100D with a 75-300mm zoom lens, using manual focus with the "full auto" mode for controlling aperture, shutter time etc. Usually I am leaning out of a window or standing in my garden to capture these shots.
As you can see, none of these images are particularly "good": the subjects in the first three images are underexposed due to their dark colouring against a light background, some are slightly out of focus, some show evidence of dirt or other marks on the camera sensor, yet you can still make out various details on all of them. One would imagine that if there were an equivalent photo of an actual "alien" UFO, it would be on the front page of newspapers across the world.
(One trick that I use for family photos is to use a delay of 1 second, to avoid the movement when I press the shutter. (It's not useful when there are kids. One second later they are in another room.))
I've been meaning to pick up a shutter release accessory for a while now since the 1100D only has 10s shutter delay in automatic modes, or 2s delay in the manual modes. Fortunately the movement when pressing the shutter button isn't much of a problem for these type of shots as the camera + lens is weighty and quite well balanced.
So I would be extremely suspicious of sharp clear properly exposed pictures of UFOs.