For your image, I found I needed to set a relatively high “Threshold” (the upper range of brightness values that LightBurn will trace) to produce a clean outline around the body. I turned up the “Ignore less than” value as well, to reduce noise/unneeded traces in the middle section of the body
Because the top of the skull is so light, I wasn’t able to get a trace around the outline there - but cleaning up just that section with node editing will be much faster than going around the entire graphic.