false by default so setting it to
false has no effect.
computeVertexNormals() has not the expected effect since the geometry is non-indexed. Meaning no vertices are shared between triangles so the surface has to look flat shaded when calling this method.
You could try to use BufferGeometryUtils.mergeVertices() to create an indexed geometry. However this function can only merge vertices if all existing vertex data match (vertices, normals, uvs, colors etc.). This makes it problematic to use it with
ExtrudeGeometry see https://jsfiddle.net/r6zguh09/1/.
It’s probably best if you create a custom cylinder mesh in Blender and import it as a glTF asset.