Import
SobelOperatorShader is an addon, and must be imported explicitly, see Installation#Addons.
import { SobelOperatorShader } from 'three/addons/shaders/SobelOperatorShader.js';Properties
.SobelOperatorShader : ShaderMaterial~Shader (inner, constant)
Sobel Edge Detection (see https://youtu.be/uihBwtPIBxM).
As mentioned in the video the Sobel operator expects a grayscale image as input.