Is there a guided tour for the new features of 1.9.19?

Yes. Press "Guide" at the bottom left. The book's page tour has steps for "Ready to publish", the folding cards, the Promise card and the "Changed since the chapters were written" card. The chapter editor tour shows "Add my story here", "Remember for later", "I have a story" and the stories waiting. The Interview tour walks through telling a story in one go, the places, and the buttons of the preview, on an example, without any AI call. The New Book tour covers the working title and subtitle. The Settings tour shows the Updates card. Under "Make it yours" in the Guide panel, "Hold the book to its promise" ticks itself once you have checked or confirmed a book's pair.