Filling area under linerenderer

In my opinion a LineRenderer is not very good for filling the area below a graph. Instead, you need a polygon whose lower vertices are aligned to the graph axes, and its upper vertices to the graph line.
In 3D you can use a dynamically created mesh, in 2D probably a sprite whose vertices you modify. Rough outline of 3D version:

 public void CreateFilledGraphShape (Vector3[] linePoints) {
     Vector3[] filledGraphPoints = new Vector3[linePoints.Length * 2]; // one point below each line point
     for (int i = 0; i < linePoints.Length; ++i) {
         filledGraphPoints[2 * i] = new Vector3(linePoints[i].x, 0, 0);
         filledGraphPoints[2 * i + 1] = linePoints[i];
     }
 
     int numTriangles = (linePoints.Length -1) * 2;
     int[] triangles = new int[numTriangles * 3]; 
 
     int i = 0;
     for (int t = 0; t < numTriangles; t += 2) {
         // lower left triangle
         triangles[i++] = 2 * t;
         triangles[i++] = 2 * t +1
         triangles[i++] = 2 * t +2;
         // upper right triangle - you might need to experiment what are the correct indices
         triangles[i++] = 2 * t + 1;
         triangles[i++] = 2 * t + 2;
         triangles[i++] = 2 * t + 3;
     }
 
     // create mesh
     Mesh filledGraphMesh = new Mesh();
     filledGraphMesh.vertices = filledGraphPoints;
     filledGraphMesh.triangles = triangles;
     // you might need to assign texture coordinates as well
 
     // create game object and add renderer and mesh to it
     GameObject filledGraph = new GameObject("Filled graph");
     MeshRenderer renderer = filledGraph.AddComponent<MeshRenderer>();
     renderer.mesh = mesh;
 }

Maybe Sprite Shape can solve this problem
At least it helped me in a similar situation

intro-to-2d-world-building-with-sprite-shape