you can do it with just a simple path that you set to a wider stroke (8 for example), then blur it to a 1% or so and also apply a mask to it. The mask object should be filled with a black and white gradient where white goes over the center areas, and black goes over the path ends to make the ends thinner.
Heres the result (2 nodes, blurred 1%, masked on the ends):
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Here is what my mask object looks like, its a rectangle with linear repeated w&b gradient. I have reduced opacity of the rectangle to 70% so you can see how its positioned over the path:
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Another way is to use Pattern along path (this method doesn't require masking):
Create a very thin and long ellipse or very thin and long rectangle with rounded corners. Copy it. Now create your path and apply Pattern along Path to it. Click on the Paste Path button there and the ellipse will be deformed along the path. All you have to do now is add fill color, remove stroke and blur it 1%.
Heres the result (on top is the ellipse I used, bellow is the path of 2 nodes with Pattern along Path applied using the ellipse, with filled color green and 1%blur):
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