I hold to the view that the Genesis story of the Flood derives either from the Epic of Gilgamesh itself or from similar myth/s. In so saying I agree with the Bible commentary of the U.S. Council of Catholic Bishops, which says:
The biblical story ultimately draws upon an ancient Mesopotamian
tradition of a great flood, preserved in the Sumerian flood story, the
eleventh tablet of the Gilgamesh Epic, and (embedded in a longer
creation story) the Atrahasis Epic.
I propose the following narrative as a way to harmonize the Mesopotamian origin of the story with the biblical account: Abraham lived in Ur of the Chaldeans, before coming to Canaan. This was a major religious center, where he would certainly have known the story of Gilgamesh. Abraham retained this knowledge and either he or his descendants recast the story, with variations, in a monotheistic form. Eventually, the gods who played various roles in Gilgamesh (one sends the flood, another warns Utnapishtim, while later the goddess Ishtar weeps for her lost children, and a whole crowd of gods gather at the end) are combined into one. The God of Abraham thus becomes the only divine character in the drama. Much later, the story would be incorporated into the text of Genesis.
The questioner of the OP says he does not not of there is an online version of the Atrahasis legend. This one is quite readable.