No credible tangible evidence has ever been presented.
All we have are unverified claims and grainy photographs and videos.
People have been claiming for decades also that they have seen Big Foot and the Loch Ness monster.
It really doesn't help the cause that so many UFO encounters, Loch Ness monster photos, and Big Foot evidence have been faked and contrived. It doesn't inspire confidence. In conventional science there is almost never any faking of data, from particle physics, to astronomy, to genetics.
There are five billion smart phones on the planet now. Surely we would have better and more convincing video of alien spaceships by now
You're making assumptions based on logic that might not apply to UFOs, so comparing them to those two hoaxes, would be pointless.
First of all, Big Foot and the Loch Ness monster are, if they exist, Earth based entities to which the physical laws of Earth apply.
They would have to be somewhere on Earth, taking up space at all times.
It would be reasonable then, to assume that if they really exist, better evidence would have been found by now.
With UFOs OTOH, we're talking about objects and/or beings from other worlds and possibly other universes, time/dimensions etc., which can seemingly appear out of nowhere and disappear into thin air.
They might possess technology that enables them to render themselves invisible to the five human senses and human recording devices, while operating right under our noses.
Because we know nothing about what lies beyond the miniscule portion of the universe we are able to observe, all we can do is guess and make assumptions.