But even then, if we knew what caused the universe to exist, we would then be looking at the cause of the universe and wondering what caused that cause to exist. And so I think we'd still be left wondering why anything exists at all at the end of the day.
They even got as far as describing God as "uncaused causality" centuries ago, which lined up pretty well with the translation of the name God reportedly gave one of their forbearers from a burning bush, "I am who am," or colloquially, "I'm the one who just is. I am being-itself, not contingent in any way, outside your concepts of 'before' or 'contingent upon.'"
If you say these are not changes, only actions, then the same can be said of the Universe: it didn't change, the rules of physics have always been the same, it just does things according to its rules.
I'm not going to pretend I have anything like the math or theoretical physics knowledge to grok the latest perspectives on whether the universe actually had a beginning or an end, or whether it goes through singularities, or any of probably a dozen other theories that I've vaguely heard of and are over my head, never mind all the ones I don't even know about. I'm not aware of any that posit the universe is truly unbound by time, though, that time is not somehow a constraint on the state of the universe such that it doesn't actually change, except from our own perspective. Is that even what you're suggesting? Or have I missed your point entirely?
But this can be done for any system just as well: instead of saying that the egg was broken to make an omlette, you could say that the egg has always been in the same state: the state where it is whole before the omlette, and broken afterwards. The egg itself is a timeless concept, but we just experience it differently as time passes for us. I don't see why this argument works for God and not for my egg.
So from our/Noah's perspective, that situation has come and gone, has changed, because we're bound by physics and the passage of time and cannot exist in that circumstance any longer. But from God's perspective, that world is always destroyed by flood. It may be the case that the criteria that categorize a world as "destroyable by flood" never exist in our experience of time again, and it may equally be the case that God knows this will be the case.
But God's willingness to destroy the world by flood under those criteria has not and will never change, because God's will does not change.