FINALLY,
In Inkjet version 1.3, (and presumably 1.2) Centerline Trace menu choice is HIDING in the
Trace Bitmap > Single Scan > Detection Mode (dropdown list).
(I upgraded to Inkscape 1.3, and did NOT install any add-ins or extensions.)

- Brian
Did a very quick successful test.
Imported to MoI. There are some gaps, and little squiggles, in the single centerline curves, but MoI can correct these.

It is first necessary to click on Layers, and select the PNG layer.
Also, in the Trace Bitmap screen, it may help to use "Adjust Threshold". Or not? It is not in the Centerline menu, just the Brightness cutoff menu.

Centerline trace of multiple overlapping curves tends to introduce "crossing over" squiggles. (Like DNA:-)
So the source PNG should be simplified to one pixel curve, or 2+ NON-overlapping curves.

The centerline trace curves are Vectors, (SVG), so there is almost no fuzziness at small zooms, unlike the PNG images.

Multiple color curves come out as single color Vector(s).