can not resolve Uncaught TypeError: vue__WEBPACK_IMPORTED_MODULE_0__.default is undefined - vue.js

Question

I am working on vue js 2 version and I needed to download font-awsome library for styling purpose. However, when I downloaded the files it seemed not compatible with my project so I deleted/uninstalled them (the font-awsome libraries), and then all of a sudden when I tried to refresh the server I got this error in the console :
Uncaught TypeError: vue__WEBPACK_IMPORTED_MODULE_0__.default is
undefined
Note that the code was working fine before installing and uninstalling the the font-awsome libraries, I don't really know what happened I also did try to ctrl + z to restore the main.js but is still showing the same error.
1- main.js:
import Vue from 'vue'
import App from './App.vue'
import router from './router'
import VueFirestore from 'vue-firestore'
import JQuery from 'jquery'
import {BootstrapVue, IconsPlugin} from 'bootstrap-vue'
import 'bootstrap/dist/css/bootstrap.min.css'
import 'bootstrap-vue/dist/bootstrap-vue.css'
import 'bootstrap/dist/js/bootstrap.min.js'
import './assets/app.scss'
import swal from 'sweetalert2';
// import VoerroTagsInput from '#voerro/vue-tagsinput';
Vue.use(BootstrapVue)
Vue.use(IconsPlugin)
window.$ = JQuery
Vue.use(VueFirestore, {
key: 'id', // the name of the property. Default is '.key'.
enumerable: true // whether it is enumerable or not. Default is true.
})
Vue.use(VueFirestore)
Vue.config.productionTip = false
// Make BootstrapVue available throughout your project
// Vue.use(createPopper)
let app = '';
if(!app){
new Vue({
router,
render: h => h(App)
}).$mount("#app");
}
window.Swal = swal;
const Toast = Swal.mixin({
toast: true,
position: 'top-end',
showConfirmButton: false,
timer: 3000
});
window.Toast = Toast;
2- index.js:
import Vue from 'vue'
import VueRouter from 'vue-router'
Vue.use(VueRouter)
const routes = [
{
path: '/',
name: 'books',
component: () => import('../components/books')
},
]
const router = new VueRouter({
mode: 'history',
base: process.env.BASE_URL,
routes
})
export default router
3- package.json:
{
"name": "vue-firebase-crud",
"version": "0.1.0",
"private": true,
"scripts": {
"serve": "vue-cli-service serve",
"build": "vue-cli-service build",
"lint": "vue-cli-service lint"
},
"dependencies": {
"bootstrap": "^4.5.3",
"bootstrap-vue": "^2.22.0",
"core-js": "^3.8.3",
"firebase": "^8.10.0",
"jquery": "^3.6.1",
"sweetalert2": "^11.4.37",
"vue-firestore": "^0.3.30",
"vue-router": "^3.6.5",
"vue2-editor": "^2.10.3"
},
"devDependencies": {
"#babel/core": "^7.12.16",
"#babel/eslint-parser": "^7.12.16",
"#vue/cli-plugin-babel": "~5.0.0",
"#vue/cli-plugin-eslint": "~5.0.0",
"#vue/cli-service": "~5.0.0",
"eslint": "^7.32.0",
"eslint-plugin-vue": "^8.0.3",
"node-sass": "^7.0.3",
"sass": "^1.55.0",
"sass-loader": "^13.1.0",
"vue-template-compiler": "^2.6.14"
},
"eslintConfig": {
"root": true,
"env": {
"node": true
},
"extends": [
"plugin:vue/essential",
"eslint:recommended"
],
"parserOptions": {
"parser": "#babel/eslint-parser"
},
"rules": {}
},
"browserslist": [
"> 1%",
"last 2 versions",
"not dead"
]
}
4- error in console: