Laravel8 Vue2 でVuexを使用するとexport 'inject' (imported as 'inject') was not foundエラー

Laravel8　Vue.jsのバージョンは2でvuexを使用したくサンプルコードを試していますが、
npm run watchで以下のエラーが出てしまいます。

WARNING in ./node_modules/vuex/dist/vuex.esm-bundler.js 14:9-15
export 'inject' (imported as 'inject') was not found in 'vue' (possible exports: default)

WARNING in ./node_modules/vuex/dist/vuex.esm-bundler.js 140:17-25
export 'reactive' (imported as 'reactive') was not found in 'vue' (possible exports: default)

WARNING in ./node_modules/vuex/dist/vuex.esm-bundler.js 345:2-7
export 'watch' (imported as 'watch') was not found in 'vue' (possible exports: default)

WARNING in ./node_modules/vuex/dist/vuex.esm-bundler.js 1078:9-14
export 'watch' (imported as 'watch') was not found in 'vue' (possible exports: default)

resources>js>app.js　は以下になりますが、★部分をコメントアウトするとこのwarnは出てこないので、このvuexがいけないのかなと思ってます。
■resources>js>app.js

import './bootstrap'
import Vue from 'vue'
//spaで追加
import router from './router'
//vuexで追加
import store from './store.js' //★コメントアウトするとwarnは出ない

//ページネーションで追加 testコメント
import Paginate from 'vuejs-paginate'

//モーダルで追加
import VModal from 'vue-js-modal';
Vue.use(VModal);

window.Vue = require('vue');
Vue.component('ShopOrder', require('./component/user/ShopOrder.vue').default);
Vue.component('ShopOrderCheck', require('./component/user/ShopOrderCheck.vue').default);
Vue.component('StripeCard', require('./component/user/StripeCard.vue').default);
Vue.component('StripeCard3', require('./component/user/StripeCard3.vue').default);
Vue.component('ShopComplete', require('./component/user/ShopComplete.vue').default);

//ページネーションで追加
Vue.component('paginate', Paginate);

//Vue.component('AccountList', require('./component/admin/AccountList.vue').default); これだと表示されない


const app = new Vue({
  el: '#app',
  router, //spaで追加
  store: store, // ストアを追加する★コメントアウトするとwarnは出ない
})

//これ何だっけ…
//require('alpinejs');

以下はpackage.jsonです。
■package.json

{
    "private": true,
    "scripts": {
        "dev": "npm run development",
        "development": "mix",
        "watch": "mix watch",
        "watch-poll": "mix watch -- --watch-options-poll=1000",
        "hot": "mix watch --hot",
        "prod": "npm run production",
        "production": "mix --production"
    },
    "devDependencies": {
        "@tailwindcss/forms": "^0.3.3",
        "@tailwindcss/typography": "^0.4.1",
        "alpinejs": "^3.2.4",
        "axios": "^0.21",
        "laravel-mix": "^6.0.6",
        "lodash": "^4.17.19",
        "postcss": "^8.1.14",
        "postcss-import": "^14.0.2",
        "tailwindcss": "^2.2.7",
        "vue-loader": "^15.9.8",
        "vue-template-compiler": "^2.6.14",
        "vuex": "^4.0.2"
    },
    "dependencies": {
        "@stripe/stripe-js": "^1.13.2",
        "@vue-stripe/vue-stripe": "^4.2.5",
        "vue": "^2.6.12",
        "vue-js-modal": "^1.3.35",
        "vue-router": "^3.5.2",
        "vuejs-paginate": "^2.1.0"
    }
}

vuexをインストールする際に無邪気に