As l see it, there are details in the story of Abraham that take it out of the realm of fiction. For instance, Abraham had a family tree that connects to figures of history. In Genesis 11:26 it says, 'And Terah lived seventy years, and begat Abram, Nahor, and Haran'.
Then we are also told where Abraham came from (Ur of the Chaldees), and where he was headed (Canaan). We also know he stopped at Haran (situated in Turkey), having travelled up beside the Euphrates river from 'the Chaldees'.
By the time we reach the story of Genesis 18, in the plains of Mamre, we already know much about Abraham, his household, and his relationship with neighbouring people. In Genesis 21, lsaac is born to Sarah, and we are told Abraham was, at that time, one hundred years old (verse 5).
We are also told about Abraham's dealings with Abimelech, and the well that Abraham dug at Beersheba, which, apparently, still exists to this day.
According to the scripture, Sarah died aged 137, and was buried in Machpelah, near Mamre. Abraham, when he reached 175 years of age was buried in the same cave by his sons, Isaac and lshmael [Genesis 25:9].
Abraham's story is set within genuine history (mentioning Chaldeans, Canaanites, Hittites, Amorites, Jebusites, Egyptians etc)
We also find Abraham mentioned elsewhere in scripture, and the references are not to a fictional character. He is mentioned in Exodus, Leviticus, Numbers, Deuteronomy, Joshua, 1 Kings, 2 Kings, 1 Chronicles, 2 Chronicles, Nehemiah, Psalms, Isaiah, Jeremiah, Ezekiel, Micah, Matthew, Mark, Luke, John, Acts, Romans, 2 Corinthians, Galatians, Hebrews, James, and 1 Peter.
The story of Abraham is, to me, a believable account. But, l acknowledge that, without a belief in God, it is hard to accept testimony of supernatural events.
Then again, the idea that the universe could have come from nothing rather than from God is, IMO, untenable. And so, as an initial premise, the miracles of God become acceptable. Why should they not continue to appear when God is involved?