Joel S. Baden, “Leviticus,” in The SBL Study Bible, edited by Steven L. McKenzie, Kristin De Troyer, and F. Scott Spencer (HarperOne, 2023), 173.
Despite having its own title, there is really no “book” of Leviticus in any meaningful sense. Leviticus never existed as an independent literary or textual unit at any stage of its development or incorporation into biblical canon. The Pentateuch is not five independent books cobbled together but rather a single literary work presented in five volumes, the division having been based on the material limits of scroll technology. The essential continuity of Leviticus with what comes before and after is apparent from both a broad perspective and from a close reading. The very first words of the book, literally “He called to Moses,” lack an explicit subject in Hebrew; the English addition of “the LORD” is assumed from preceding verses at the end of Exodus. Who Moses is, where and when the events of Leviticus take place, what the nature and historical background of the relationship between Israel and its deity is – none of these are explained in Leviticus itself but are dependent on the story that has been told from the beginning of the Pentateuch to this point.
The Amateur Exegete 
Interesting. Now, does Baden address WHY the division is where it is?
Exodus 35, after the second giving of the tablets of the Ten Divarim, gets to Yahweh’s instructions for the tabernacle, the ark of the covenant and such. Breaking Exodus after chapter 34 and attaching the rest to Leviticus makes much more sense.
Otherwise, I would disagree with part of the take. Leviticus’ start isn’t dependent on the whole Torah up to that point. Rather, to riff on Tatian, you can see Genesis, then a Tessarateuch after that, so to speak. Or Genesis, Triteuch and Deuteronomy, especially if you plump for some version of the documentary hypothesis.
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