On a finalize event, the event doesn't seem to have event.clientX and event.clientY properties, to get the coordinates of the element where it is dropped.
The closest I could find is event.target.clientLeft and event.target.clientTop, but they are always 0, it seems to be the width of the border.
I am attempting an implementation with svelteflow:
https://stackblitz.com/edit/svelte-dnd-action-svelteflow