I have nothing written at hand. Can BookyAI still learn my voice?

Yes, from version 1.9.18. On the Authors page, in the "Author voice" card of your profile, press "Build my voice by interview". BookyAI asks you a few easy questions about your work, one at a time, and you answer the way you would talk to a friend: long and loose. It learns from how you answer, not from what you say. When you have written enough (at least 40 words, more is better), press "Teach my voice from this": your answers are added as a sample. Then press "Learn my voice" on the card.