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 Squarespace account, no export file and no API key. If Chrome can draw the page, wpgraft can copy it.
Squarespace’s WordPress export carries your content and drops your design. wpgraft is the missing half: it copies the design from the published site, Fluid Engine grid sections and all, and rebuilds it as Elementor elements. Run the two together and you leave with both.