Can I regenerate all the chapters of my book at once, instead of one by one?

Yes, from version 1.9.21. Open the book's page and, above the chapter list, press "Regenerate all". A window asks where the new text goes, "In this book" or "In a copy of this book", and which AI engine writes it. Press "Regenerate" and BookyAI writes every chapter again, one after another, from the same outline: the chapter titles and the instructions you gave each chapter stay the same. In this book, every chapter's current text is kept first in its Versions panel, so you can always go back. A chapter that fails keeps its old text, and you can stop at any time. The front and back matter (preface, glossary and the like) is marked to refresh afterwards, in its own card.