Can you see the cutting line in Inkscape?
The auto-trace engine cannot pick out the cutting line from your image. No trace engine that I know of could do that. You could use Inkscape's Pen tool, and your own eyes, to see the cutting line and draw it. In your 2nd message above (message #3) you gave a link to a screenshot where there's an image on the left - a single, solid, black line.
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