David Bokovoy summarizes the evidence for Isaiah 40-66 being written during/after the exile; argues the presence of some of these chapters in the Book of Mormon is an anachronism.
David Bokovoy, “Prophets and Prophetic Literature,” in The Bible and the Latter-day Saint Tradition, ed. Taylor G. Petrey, Cory Crawford, and Eric A. Eliason (Salt Lake City: The University of Utah Press, 2023), 390-92
ISAIAH AND THE BOOK OF MORMON
One of the most significant challenges for traditional LDS readings of prophetic material is the fact that this literature grew over time and was most likely not produced by the men whose names are connected with the biblical books. This is especially true for the composition of Isaiah. Since the twentieth century, virtually all mainstream scholars have held the position that Isaiah chapters 40-66 were written after the Jewish exile into Babylon (c. 586 BCE). This means that the historical Isaiah, a prophet who lived in Jerusalem during the eighty century BCE, did not write the second half of the book of Isaiah. For Latter-day Saints, this presents a direct challenge for traditionally held paradigms concerning the Book of Mormon since some of its material attributes these later chapters to Isaiah himself. If scholars are correct, then this material would not have been available to the Book of Mormon people because it was not written until after they had arrived in the New world. Its attestation in the Book of Mormon is therefore anachronistic.
There are several compelling reasons scholars argue that Isaiah 40-66 is not a prophecy given by the historical Isaiah. Amongst other points, these factors include the following: (1) First Isaiah mentions Isaiah son of Amoz and provides biographical material regarding him and others of his time whereas the material in Second and Third Isaiah makes no mention of his name; (2) Deutero-Isaiah provides a polemical response to the Cyrus Cylinder and mentions the Persian ruler by name; (3) the historical Isaiah of the eighth century believed in the inviolability of Jerusalem and the authors of 40-66 present a message of comfort to the Judean exiles that directly counters Isaiah’s theological conviction; (4) the authors of 40-55 know the alter-prophetic work of Jeremiah, but Jeremiah shows no signs of knowing the Deutero-Isaiah prophecies; (5) the authors of 40-66 knew exilic and postexilic material including Lamentations; (6) Deutero-Isaiah shows signs of Aramaic and Post-Exilic Hebrew influence (but this same linguistic trace does not appear in the oracles of the historical Isaiah).
Any one of these issues would be enough to convince biblical scholars that Isaiah 40-66 is postexilic material added to Isaiah proper. All of them together provide undeniable evidence for the scholarly consensus. Exactly how and why later scribes attached these oracles to those of an earlier prophet is unknown. Yet contemporary scholars are certain that 40-66 does not reflect the work of the eighty century Isaiah son of Amoz. LDS apologetic responses to this challenge typically approach the topic by focusing on the Book of Mormon as a revelatory work given through Joseph Smith. In creating the Book of Mormon, Smith did not simply work his way line upon line through an ancient script carved into golden plates. The translation of the Book of Mormon was more likely a revelatory, creative experience similar to the adaptation of scriptural sources seen in earlier biblical and post biblical traditions. Mormon scholars argue that Latter-day Saints should expect that the book would contain inspired prophetic, midrashic use of material known to Smith, including the material in Isaiah 40-66.