如下图

可能原因，没有灯光，加下以下代码：

// 4、加入灯光
const lightness = new THREE.HemisphereLight(0xffffff, 0x444444);
lightness.position.set(0, 20, 0);
scene.add(lightness);
const shadowLight = new THREE.DirectionalLight(0xffffff);
shadowLight.position.set(0, 20, 10);
scene.add(shadowLight);

实现效果

renderer.outputEncoding = THREE.sRGBEncoding;

loader.load("./model/牛角面包.glb", function (gltf) {
    gltf.scene.scale.set(20, 20, 20);
    scene.add(gltf.scene);
})