I design my back cover text in Canva or KDP Cover Creator. Can I get the back cover without text?

Yes. From version 1.9.17, click "Text" under the back cover and untick "Put the description and the author bio on the back cover". The back cover is then the artwork alone. BookyAI always keeps the artwork without text on its own, so switching the text on or off, or changing the words, never costs a new image generation. A back cover that you uploaded yourself or picked from the gallery is treated as a finished design: BookyAI adds no text to it unless you switch the text on.