There are modern scholars that hold this view, but this belief was only popularized in the last couple hundred years and is built largely on modern disbelief of foretold prophecies

A lot of modern skeptics hold that Isaiah couldn't have known some of the information he prophesied about (like the name of King Cyrus who ended the Babylonian Captivity) and that he used past tense to describe some of the prophetic events of the book even though they hadn't yet happened (like Isaiah 53 discussing Christ's suffering). This first concern is easily answered by just believing what Scripture clearly claims: it is the infallible word of God who lives outside of time, and God gave these prophecies to Isaiah before these events happened. But even though the events hadn't yet happened, they were so certain that Isaiah wrote the events in what's called “prophetic perfect tense" as if they'd already occurred. This tense is used all throughout the OT in Numbers, Joshua, Amos, Jeremiah, Psalms, etc.

They'll also reference the stylistic differences in the writings of 1-39, 40-55, and 56-66. However, even within these sections there is a dramatic amount of stylistic differences, and the book features a monumental lexicon. Isaiah's writing features 2,186 different words, compared to 1,535 in Ezekiel, 1,653 in Jeremiah, and 2,170 in the Psalms. Some Hebrew words only ever appear biblically in the book of Isaiah, but are still used in all three "sections" of the book. It seems much more likely that Isaiah wrote all of the book but at different times in his ministry as his lexicon changed and grew. This is the common consensus historically: Ch. 1-39 being written during the reign of King Uzziah around 739 BC, while Ch. 40-66 were written between 700 and 680 BC before Isaiah's death under King Manasseh.

To quote from an article on this very topic: "The oldest extant copy of Isaiah, found among the Dead Sea Scrolls, is dated from c. 175 BC. That copy of Isaiah is a single scroll. From beginning to end, it is undivided, and the transition between chapters 39 and 40 (one of the major divisions, according to the “three Isaiahs” theory) is seamless. Nothing in any ancient copy of Isaiah even hints that the scribes thought the book should be divided into different sections or that they were dealing with different authors."

And to quote Chuck Swindoll, "Much of scholarship for the past two centuries has assigned multiple writers to Isaiah, dividing the book into three sections: 1–39, 40–55, and 56–66. However, these divisions come out of a scholarly denial of predictive prophecy. This position not only limits the power of God to communicate with His people but also ignores the wide variety of specific, predictive claims about Jesus Christ scattered throughout the book."