I’ve tried the resample curve node, which itself increases the number of points on each hair, but doesn’t change their position to result on a smoother profile. I tried then adding a smooth hair curves node afterwards, but that seems to make it approach a straight line, even at high resample counts, rather than actually smoothing.
The only thing that accomplishes a proper smoothing is changing the Additional Subdivisions setting for curves on the render settings, but that acts for all curve objects in the scene. I’m searching for a geo nodes setup that accomplishes that type of smoothing.