i am sure it has been suggested here before and I guess you did already read it since it covers exactly that topic: interaction with alien civilization. Liu Cixin´s trilogy "Remembrance of Earth's Past" (1.The Three-Body Problem, 2.The Dark Forest, 3.Death's End) is a fantastic read
I'm reading that right now. The Chinese aspect is also interesting, with the cultural revolution, etc.
there is no doubt in my mind that life exists not only on earth. much less abundant, but in an universe of endless size that doesn't really matter, would be not just primitive life but technical advanced civilizations. imho the problem is the size of the universe. there could be millions of civilizations way too far away for any interaction. the other problem is time. given just the 14 billion years our universe is thought of being old, it is very unlikely to have another civilization synchronized to our technical progress.
With technology we know/can envision it seems possible for humanity to become a multi planet species. Not really easy, but possible. With advances in robotics especially, allowing resources to be gathered autonomously, it will get easier. So at first glance I have to think that other similar species, but with some millions/billions years on us, must have conquered significant parts of galaxies.
It doesn't mean it would be that easy to see, I know all the concepts of stuff like the Dyson sphere, but it's not obvious to me a civilization would go that far. Humanity is used to expand rapidly, consuming resources at a fast pace, but I could see things slowing down. If today all women on the planet didn't make more than two kids, it would make no difference in technological advancement of our species, but it would mean we can all fit on this planet. There would still be a drive to reach the stars, at least from some people, some of which have the will to do it (Elon Musk comes to mind), but let's say we find a Earth 2 not too far away, how many people would be willing to go there ? A few millions at most, if here is still a nice enough place. A few millions people on Earth 2 with our current/better tech, science, culture etc., they wouldn't start making babies like rabbits, there would probably never be any need to go elsewhere (until the end of the star). So expanding across part of a galaxy might take millions/billions of years after all.
Then there are other aspects of technology that would change the outcome completely. For example the interface between man and machine (something else Elon is working on). If one day we can "virtualize" our minds, become machines, or just information on a network, infinitely intelligent, maybe expanding across a galaxy wouldn't make any sense to us at all.