How to blur a background Texture?

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Here is a complete live example: Edit fiddle - JSFiddle - Code Playground

And the plain code:

let camera, scene, renderer;

init().then( render );

async function init() {

  camera = new THREE.PerspectiveCamera(70, window.innerWidth / window.innerHeight, 0.01, 10);

  scene = new THREE.Scene();
  
  renderer = new THREE.WebGLRenderer({antialias: true});
  renderer.setPixelRatio(window.devicePixelRatio);
  renderer.setSize(window.innerWidth, window.innerHeight);
  document.body.appendChild(renderer.domElement);

  const loader = new THREE.TextureLoader();
  const texture = await loader.loadAsync('https://threejs.org/examples/textures/uv_grid_opengl.jpg');
  //scene.background = texture;

  scene.background = blurTexture( texture );

}

function blurTexture(texture) {

  const width = texture.image.width;
  const height = texture.image.height;

  const cameraRTT = new THREE.OrthographicCamera(-1, 1, 1, -1, 0, 1);
  const sceneRTT = new THREE.Scene();

  // render targets

  const renderTargetTemp = new THREE.WebGLRenderTarget(width, height);
  const renderTargetFinal = new THREE.WebGLRenderTarget(width, height);

  // shader materials

  const hBlurMaterial = new THREE.ShaderMaterial({
    vertexShader: THREE.HorizontalBlurShader.vertexShader,
    fragmentShader: THREE.HorizontalBlurShader.fragmentShader,
    uniforms: THREE.UniformsUtils.clone(THREE.HorizontalBlurShader.uniforms)
  });

  hBlurMaterial.uniforms.tDiffuse.value = texture;
  hBlurMaterial.uniforms.h.value = 1 / width;

  const vBlurMaterial = new THREE.ShaderMaterial({
    vertexShader: THREE.VerticalBlurShader.vertexShader,
    fragmentShader: THREE.VerticalBlurShader.fragmentShader,
    uniforms: THREE.UniformsUtils.clone(THREE.VerticalBlurShader.uniforms)
  });

  vBlurMaterial.uniforms.tDiffuse.value = renderTargetTemp.texture;
  vBlurMaterial.uniforms.v.value = 1 / height;

  // fullscreen quad

  const planeGeometry = new THREE.PlaneGeometry(2, 2);

  const fullScreenQuad = new THREE.Mesh(planeGeometry, hBlurMaterial);
  sceneRTT.add(fullScreenQuad);

  // first pass

  renderer.setRenderTarget(renderTargetTemp);
  renderer.render(sceneRTT, cameraRTT);
  renderer.setRenderTarget(null);

  // second pass

  fullScreenQuad.material = vBlurMaterial;

  renderer.setRenderTarget(renderTargetFinal);
  renderer.render(sceneRTT, cameraRTT)
  renderer.setRenderTarget(null);
  
  //
  
  return renderTargetFinal.texture;


}

function render() {

  renderer.render(scene, camera);

}
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