main.js

// Load Synty Studio art pack FBX models with THREE.js
// Remarks:
// * Assumes the POLYGON City pack in subdirectory models/PolygonCity, adjust directories and filenames as you need
// * Relies on submesh naming conventions to assign glass material; if it doesn't work for your FBX, double-check that the glass actually ends with "_Glass"
// * Uses async/await to improve the readability and traceability of the program flow

// Standard THREE initialization code

import * as THREE from 'three'
import { FBXLoader } from 'three/examples/jsm/loaders/FBXLoader'
import { TGALoader } from 'three/addons/loaders/TGALoader.js'
import { OrbitControls } from 'three/examples/jsm/controls/OrbitControls'

const scene = new THREE.Scene()
const camera = new THREE.PerspectiveCamera(75, window.innerWidth / window.innerHeight, 0.1, 1000)

const renderer = new THREE.WebGLRenderer()
renderer.setSize(window.innerWidth, window.innerHeight)
document.body.appendChild(renderer.domElement)

camera.position.z = 50

// We need a light, too

const light = new THREE.DirectionalLight(0xffffff, 1)
light.rotation.z = 45
scene.add(light)

// Let's allow orbiting around the imported mesh

const controls = new OrbitControls(camera, renderer.domElement)
controls.enableDamping = true
controls.target.set(0, 0, 0)

// Create material and load model

const textureLoader = new THREE.TextureLoader()
const albedo = await textureLoader.loadAsync('models/PolygonCity/Textures/PolygonCity_Texture_01_A.png')
const normal = await textureLoader.loadAsync('models/PolygonCity/Textures/PolygonCity_Texture_Normal.png')

const tgaLoader = new TGALoader()
const metalness = await tgaLoader.loadAsync('models/PolygonCity/Textures/PolygonCity_Texture_Metallic.tga')

const material = new THREE.MeshStandardMaterial({
	map: albedo,
	normalMap: normal,
	metalnessMap: metalness,
})

const glass = new THREE.MeshStandardMaterial({
	color: '#049ef4',
	transparent: true,
	opacity: 0.5,
})

const fbxLoader = new FBXLoader()
const mesh = await fbxLoader.loadAsync('models/PolygonCity/Models/SM_Veh_Car_Van_01.fbx')
mesh.traverse((child) => {
	if (child.isMesh) {
		if (child.name.endsWith('_Glass')) {
			child.material = glass
		} else {
			child.material = material
		}
	}
})

scene.add(mesh)

function animate() {
	requestAnimationFrame(animate)
	renderer.render(scene, camera)
}
animate()

Result: