Emanuel Swedenborg (1688-1772), whose teachings are accepted in the various "New Church" or Swedenborgian denominations, stated that all of the early stories of Genesis up to the point of Eber in Genesis 11:14-16 are purely symbolic.
In the introduction to his interpretation of Genesis 11 he states:
The historical events mentioned up to now, apart from those concerning Eber, are not true but made-up. This can be be seen from the details given in this chapter concerning the tower of Babel. (Arcana Coelestia #1283)
Elsewhere in the same work he makes several similar statements:
From here [Genesis 5:1] down to Eber in chapter 11 the names used nowhere mean actual persons, but real things. (Arcana Coelestia #470)
Everything put together as history from Genesis 1 down to Eber in chapter 11 means something different from what appears in the literal meaning, and . . . the historical narratives there are purely made-up history, which was customary among the most ancient people. (Arcana Coelestia #1020)
This chapter [Genesis 10], and the next as far as Eber, continue the most ancient style . . . The names in this chapter, apart from Eber and his descendants, are used to mean just so many nations - just so many nations as constituted the Ancient Church, a Church that was spread abroad widely throughout areas surrounding the land of Canaan. (Arcana Coelestia #1140)
From Genesis 1 down to this point [Genesis 12:1], or rather, down to Eber, the narratives have not consisted of true history but of made-up history, which in the internal sense meant things that are heavenly and spiritual. In this and subsequent chapters, however, they are not made-up but true historical narratives, which in the internal sense in like manner mean things that are heavenly and spiritual. This may become clear to anyone simply from the consideration that it is the Word of the Lord. (Arcana Coelestia #1403)
Swedenborg, like many other commentators, saw Eber as the father of the Hebrew nation:
These [the sons of Joktan listed in Genesis 10:26-29] were just so many nations consisting of the families of Eber. This becomes clear from their condition at that time. As stated already, in the most ancient times nations lived distinguished into separate families, and families into houses. Each nation recognized one father from whom it took its name. When the sons of one father multiplied, they in a similar way constituted houses, families, and nations, and so on; as did those who were the sons of Joktan. This becomes clear from the sons of Jacob who at a later time when they multiplied constituted tribes, each one of which recognized as its father, and took its name from, one of the sons of Jacob. But taken all together they were descended from Jacob, and were called Jacob. In the same way these nations were descended from Eber and were called the Hebrews. (Arcana Coelestia #1246, italics added)
Though Swedenborg considered Eber to be the first real, non-symbolic person in the Bible, from there to Terah, Abraham's father, there is only a genealogy, with no stories attached to the names. Terah's story is told in Genesis 11:24-32. By the time the stories of Abraham begin in Genesis 12, the style of the Biblical narrative has shifted decisively from its earlier mythical and symbolic style to a much more historical style.
Because of all of this, present-day Swedenborgians generally consider real, non-symbolic (non-allegorical) people to start somewhere between Eber and Abraham.
However, I should add that even after that point, Swedenborg and Swedenborgians still consider the Bible narrative to have a symbolic, spiritual meaning. And many present-day Swedenborgians do not think it is necessary to insist that the events described in the Bible from Genesis 12 onward took place historically exactly as described in the Bible narrative.