“What absolute proof is there that there is life more advanced than humanity on another planet?”
You’re putting the cart before the horse. First, you need to ask if we have any proof that there is any kind of life, even microbes, on another planet. The answer to that question is no, although we suspect there may be somewhere.
So if we don’t even have evidence of any life originating elsewhere from Earth, we certainly don’t have evidence of life more advanced than humanity.
The laws of probability suggest there is likely some life somewhere else other than Earth, but until we find something to prove that, it’s just a theory.