wpgraft reads the page as your browser rendered it, every element and the computed styles on each one, at every breakpoint you ask for, and rebuilds it as Elementor’s own native elements with the styles in Elementor’s own fields. It needs no access to your Wix account, no export file and no API key. If Chrome can draw the page, wpgraft can copy it.
Wix gives you no way to export a design, so leaving it has always meant rebuilding from screenshots. wpgraft copies from the published Wix site instead, section by section, and rebuilds each one as Elementor elements. Take the design across first and keep the Wix site live until the new one is genuinely better. The two never have to be aware of each other.