Path Difference

I was trying to set the path difference in the second image.
According to my plans theoretically he should left the circle intact, cutting and shaping only the line

...but...

When I go to path set difference then it "erase" the line and the circle.

Why?

I don't know Inkscape very well, so can you describe me each step to make?
✨ thanks for your helpful help! ✨

Path Difference

I was trying to set the path difference in the second image.
According to my plans theoretically he should left the circle intact, cutting and shaping only the line

...but...

When I go to path set difference then it "erase" the line and the circle.

Why?

I don't know Inkscape very well, so can you describe me each step to make?
✨ thanks for your helpful help! ✨

_{Ps: if you think this question is useful and well written, do not hesitate to put an upvote, thanks}