WordPress is for making web pages. While you could convert a web page in whole or in part into a book cover, the final product’s graphic quality could suffer. I’d expect most would prefer to use a proper graphics editor package, e.g. Photoshop and the like. Users could upload their preferred cover graphics file. You could specify acceptable file formats, resolution, color space, etc. needed to produce the final graphic.
TBH, if I were seeking such a service and was forced to use Elementor to produce my graphic instead of my favorite graphics editor, I’d go elsewhere. But that’s just me. Perhaps your customer base is different.
