Uncaught TypeError: Cannot read properties of undefined (reading ‘prototype‘)

You may not believe it This question is really yours vue The version is too high
It is not recommended that you reduce vue edition
You can easily introduce element-plus

npm install element-plus --save

then main.js Refer to the code

import {
    createApp} from 'vue'
import App from './App.vue'

import ElementPlus from 'element-plus';
import 'element-plus/dist/index.css';

createApp(App).use(ElementPlus).mount('#app')

And then in App.vue Write a element ui Component try

<template>
  <div id = "app">
      <el-button icon="el-icon-plus" size="small"> I am a element-plus Button </el-button>
  </div>
</template>

<script> export default {
       name: 'App', } </script>

<style> </style>

The effect is also very good