As far as "what is factual" - is an ongoing debate. At one time they believe that King David wasn't factual until they found evidence of King David. Then they though that the size of his kingdom wasn't factual, until the discovered an outpost at the furthest point of his kingdom.
In other words, archaeology that confirms the factual vs non-factual is painstakingly long and science continues to correct itself. What we do know is that many archaeologists use the Bible to find thins like this:
A recent discovery that validated the two mountains where one declared blessings on one mountain and on declare curses on the other. One could say "myth" until they found it. It is no longer a myth.
So what are we left with? Consistency of evidence and "potential" realities that have yet to be proven. It doesn't mean it is but a myth since the the consistency of what we find corroborate the history given.
So, my personal viewpoint, which you can have a different viewpoint:
Genesis 5 - notice the detail that is repeated in Luke 3. One doesn't usually find myths having actual genealogies. I find that to be true. You don't have to agree, but there is no reason for me not to believe the accuracy of the genealogy.
Before I move on... I have touched on one item that I believe can be factual in Genesis. (Don't want to put too many items at the same time)