I have a very simple stylized M character traced into an object. I want that to be satin stitched. But when I select "Inkspace - Convert line to Satin" it throws me the error of "'Only simple lines may be converted to satin columns."

How can I convert this shape to, as it says - simple lines --so I can sating stitch it? Or rails?

That convert line to satin seems to only work on shapes created using the Inkscape tools. Like the stroke around a box. I've asked about this before and was told to break my object into pieces (Path > Break Apart). From there, you're supposed to create a running line, but I've never gotten that far. Research these operations and you might figure out a process that works.👀

There are several ways of breaking the shape apart (path > break apart won't help here much). Here (the image) is just one way to do it. As said, embroidery adds dimension to flat images. This means, you have to add additional structure. Automated solutions are not always the best idea in that matter, because the algorithm couldn't really understands where and how to fill in the "missing information" best.

You can break apart node based, but I think the easiest way to handle this, is to actually redraw. That way you can handle the routing along with the push and pull compensation while drawing. Push and pull for satins means, making the satins thicker along the rails and go short at start and end. https://inkstitch.org/tutorials/push-pull-compensation/

It's a bit of work, but it really will help to learn how embroidery actually works.

Edit: Nr. 11 isn't really the best idea I ever had. It would be on top of the satin... So that part may need to be broken apart as well to get back to 12.