I will start with the caveat that our understanding of possible life on other planets is limited by our own experiences here on earth. We do not know what we do not know. Our minds tend to think in the construct of what humans have experienced here on earth.
I once subscribed to the theory that there are an infinite number of planets in the universe, therefore, there must be intelligent life on an infinite number of planets in the universe. And this still may be true. It is hard to imagine a universe with so many planets and life only began on 1.
On the other hand, just because there is life on other planets does not mean it would be easy for them, no matter how intelligent, to find us. It would be like finding the proverbial needle in a haystack and the haystack is the size of a large planet. Also, the nearest planets capable of supporting life, as we know it, are many light years away. So let's say there is intelligent life on a planet 200 light years from earth. That's 200 years to get here traveling at the speed of light, which according to Einstein is not possible. Perhaps beings smarter than us have figured out a way around that. Perhaps traveling through wormholes is possible, or bending space and time is possible. It is still such a difficult problem to solve. Still, the universe is very old and there are many planets older than earth so we can assume that on some planets life began before life on earth and that life on those planets is more evolved. It is also possible beings may have developed that are just smarter than humans.
The question is, a species that is capable of interstellar travel, having overcome all the issues with relativity, is probably nothing like humans. How could we even hope to understand how they think, what culture they developed, or their societal norms. Every concept of human behavior gets thrown out the window. If you want to know why they are here, and why they have not made formal contact, how could we possibly answer those questions not knowing anything about them?
I don't know if UFOs are real, but I lean towards no, simply because the problems of interstellar space travel are so difficult to solve and the vastness of space is so incomprehensible. Also, think about this, the radio was invented in the late 1800s and serious radio transmissions did not begin for many years after that. That means a planet 200 light years from earth would still not yet receive our radio transmissions. How would they even know we are here? I can't explain the UFO sightings we are seeing recently, but I am inclined to believe it is something other than space travelers from a distant planet.
Then again, if some alien races has figured out how to manipulate gravity, then they could literally bend space making interstellar travel possible.
