Is there a guided tour of the relationships and the Mystery board in BookyAI?

Yes, from version 1.9.22. Open the Guide with the button at the bottom of the sidebar and find, among the tours about your book, "Relationships, in depth" and "The Mystery board". Each one opens the Codex on your most recent book and explains every control, step by step: for relationships the map, the timeline, feelings, changes, romance moments and secrets; for the Mystery board the sealed solution, the suspicion chart, fair play, suspects, clues and red herrings, planning and checking. Steps that need something your book does not have yet, such as two character cards, are skipped.