My manuscript is divided into "Part One", "Part Two" and so on. Will BookyAI keep the parts when I import it?

Yes, from version 1.9.24. When you import a manuscript (Library, Import), headings such as "Part One" or "Part I: The Ranch" are recognized as parts instead of becoming chapters. On the import screen, a part's row says "Part" in the list on its right, and the chapters under it are indented. You can set any row to "Part" yourself in that list; the text under a part's heading becomes the few lines printed on the part's page. In an older version, part headings came in as chapters: import the manuscript again with version 1.9.24, or delete those chapters and add the parts with "Add part here" on the book's page.