There is a curve. In the settings of its geometry, we make Bevel, creating a volume with some kind of profile (in the example on the screenshots, the type is simply Round). Also, assign different radii to the vertices, varying the thickness of the shape. Unfortunately, as a result, the geometry on the circle around the vertex is angular. And here is the question: is it possible to somehow achieve a smooth exit of geometry from the vertices, and not a sharp decline or rise? (as in the second screen, green outline)
It's a bit angular because of the interpolation method of the radius. But you can change that in properties/object data/active spline/radius:
4 identical curves. I like Cardinal or Ease interpolation here.
Another option here, for even more control, is to specify a taper curve, in properties/object data/geometry/taper object rather than using radius.