I’ll tell you in more detail I generate

[opaque sun]

I start a thread as the other discussion got a bit our of hand.

If you are not generating the mesh each from (if the spline is not changed), then doing a sedcond mesh generation for a flat line is ok.
Or, you can re-render your cylinder, and push the vertices outwards + add a fresnel effect in opacity.

[unreal steeple]

as an example here is something like this i would like to get

the central white part is the 3d cone

I want to get only the green part inside

like this

I generated this example flat along the spline (similar to LineRenderer ), but with a large number of splines, devices will die

[unreal steeple]

Spline is changed in runtime

And mesh regenerating