Certainly a lot of the “historical narrative” parts of the Old Testament–the Books of Samuel and the Books of Kings; the Books of Chronicles–do seem to bear some passing resemblance to actual history. So, for example, 2 Kings chapters 18, 19, and 20 give an account of the reign of King Hezekiah of Judah, including an attack by King Sennacherib of Assyria. And there is in fact extra-biblical evidence of the existence of a King Hezekiah of Judah, whose kingdom was attacked by King Sennacherib of Assyria, in the form of a historical artifact called Sennacherib’s Annals, or Sennacherib’s Prism. (Just as we may not totally accept the Biblical account of what happened at face value, we equally may take Sennacherib’s description of what happened–of what a glorious victory he achieved and what a crushing defeat he inflicted and so on–with a grain of salt as well.)
Similarly, there is a lot of scholarly debate about how all the pieces of the Book of Isaiah came together, with talk of different parts of that book having been written at different times by different people (the “Proto-Isaiah” and the “Deutero-Isaiah” and the “Trito-Isaiah”), but I think most people would agree that there really was an Israelite religious leader named Isaiah who lived in the 7th and 8th centures BCE.
And then of course you have things like Psalms or Proverbs–we may perhaps question whether or not the historical King David really personally wrote Psalm number so-and-so, or whether or not the historical King Solomon really had anything to do with writing or collecting this or that part of Proverbs that’s traditionally ascribed to him, but obviously these poems and sayings do exist, nor were they made up by the medieval Church or anything like that–they truly are ancient.
On the other hand, the Books of Ruth, Esther, Job, Jonah, or Daniel, while ostensibly historical narratives about real people who actually existed, may in fact be entirely fictional. Where “Hezekiah” or “Isaiah” are in the same category as “Charlemagne” or “Augustine of Hippo”, “Ruth”, “Esther”, “Job”, “Jonah”, and “Daniel” may all be the same category as “Sherlock Holmes” or “Huckleberry Finn”. In some cases, their original authors may not have even been trying to write history–it’s entirely possible the Book of Jonah, say, was self-consciously written as a fictional narrative (albeit one with a definite didactic purpose, and a message about the universality of God’s grace).