I want to convert a line element to an object in Inkscape and add a stroke to this object without fill. How can I do that?
Increase your stroke width to the wanted element width
Convert your stroke to a path
Give a new, narrower stroke to your new object and remove its fill. Ready.
See the following cartoon:
1 = the original stroke
2 = the wide stroke
3 = converted to path, the fill is removed, selected a narrow stroke