I try 2-3 ways to create a smooth surface such as Curve Network, Rail Revolve …
But, The surface is not smooth. It’s have edge X-Cross appear on my surface
One way could be this:
Try making a planar surface, rebuild it with 4x4 uv points, grade 3 and pull up the 4 inner control points.
From there you can rebuild it with more points and move them (always symmetrycally) to refine further the shape