some bare minimum to get vue3 boot (no UI yet)

src/App.js

@@ -46,7 +46,7 @@ export default {
     this.$store.dispatch('setOption', { name: 'interfaceLanguage', value: val })
     window.addEventListener('resize', this.updateMobileState)
   },
-  destroyed () {
+  unmounted () {
     window.removeEventListener('resize', this.updateMobileState)
   },
   computed: {

src/boot/after_store.js

@@ -1,7 +1,13 @@
-import Vue from 'vue'
-import VueRouter from 'vue-router'
-import routes from './routes'
+import { createApp } from 'vue'
+import { createRouter, createWebHistory } from 'vue-router'
+import VueClickOutside from 'v-click-outside'
+
+import { FontAwesomeIcon, FontAwesomeLayers } from '@fortawesome/vue-fontawesome'
+
 import App from '../App.vue'
+import routes from './routes'
+import VBodyScrollLock from 'src/directives/body_scroll_lock'
+
 import { windowWidth } from '../services/window_utils/window_utils'
 import { getOrCreateApp, getClientToken } from '../services/new_api/oauth.js'
 import backendInteractorService from '../services/backend_interactor_service/backend_interactor_service.js'
@@ -366,25 +372,32 @@ const afterStoreSetup = async ({ store, i18n }) => {
   getTOS({ store })
   getStickers({ store })
 
-  const router = new VueRouter({
-    mode: 'history',
+  const router = createRouter({
+    history: createWebHistory(),
     routes: routes(store),
     scrollBehavior: (to, _from, savedPosition) => {
       if (to.matched.some(m => m.meta.dontScroll)) {
         return false
       }
-      return savedPosition || { x: 0, y: 0 }
+      return savedPosition || { left: 0, top: 0 }
     }
   })
 
-  /* eslint-disable no-new */
-  return new Vue({
-    router,
-    store,
-    i18n,
-    el: '#app',
-    render: h => h(App)
-  })
+  const app = createApp(App)
+
+  app.use(router)
+  app.use(store)
+  app.use(i18n)
+
+  app.use(VueClickOutside)
+  app.use(VBodyScrollLock)
+
+  app.component('FAIcon', FontAwesomeIcon)
+  app.component('FALayers', FontAwesomeLayers)
+
+  app.mount('#app')
+
+  return app
 }
 
 export default afterStoreSetup

src/main.js

@@ -1,6 +1,4 @@
-import Vue from 'vue'
-import VueRouter from 'vue-router'
-import Vuex from 'vuex'
+import { createStore } from 'vuex'
 
 import 'custom-event-polyfill'
 import './lib/event_target_polyfill.js'
@@ -21,34 +19,18 @@ import pollsModule from './modules/polls.js'
 import postStatusModule from './modules/postStatus.js'
 import chatsModule from './modules/chats.js'
 
-import VueI18n from 'vue-i18n'
+import { createI18n } from 'vue-i18n'
 
 import createPersistedState from './lib/persisted_state.js'
 import pushNotifications from './lib/push_notifications_plugin.js'
 
 import messages from './i18n/messages.js'
 
-import VueClickOutside from 'v-click-outside'
-import PortalVue from 'portal-vue'
-import VBodyScrollLock from './directives/body_scroll_lock'
-
-import { FontAwesomeIcon, FontAwesomeLayers } from '@fortawesome/vue-fontawesome'
-
 import afterStoreSetup from './boot/after_store.js'
 
 const currentLocale = (window.navigator.language || 'en').split('-')[0]
 
-Vue.use(Vuex)
-Vue.use(VueRouter)
-Vue.use(VueI18n)
-Vue.use(VueClickOutside)
-Vue.use(PortalVue)
-Vue.use(VBodyScrollLock)
-
-Vue.component('FAIcon', FontAwesomeIcon)
-Vue.component('FALayers', FontAwesomeLayers)
-
-const i18n = new VueI18n({
+const i18n = createI18n({
   // By default, use the browser locale, we will update it if neccessary
   locale: 'en',
   fallbackLocale: 'en',
@@ -75,7 +57,7 @@ const persistedStateOptions = {
     console.error(e)
     storageError = true
   }
-  const store = new Vuex.Store({
+  const store = createStore({
     modules: {
       i18n: {
         getters: {