Console error "Target container is not a DOM element." when rendering React?

Question

React

When rendering this JSX code, it gives an error in the console.
How can I fix it? I read that you need to add a script tag with a source to a js file in HTML, it did not help

Uncaught Error: Target container is not a DOM element.
    at Object.render (react-dom.development.js:26086)
    at eval (index.jsx:9)
    at Object../src/index.jsx (bundle.js:19)
    at __webpack_require__ (bundle.js:133)
    at bundle.js:156
    at bundle.js:158

import React from 'react';
import ReactDOM from 'react-dom';

let block = document.querySelector('#app')

let content = <h2>Send</h2>

console.log('hi')

ReactDOM.render(content, block)

webpack.config.js:

const path = require('path')
const HtmlWebpackPlugin = require('html-webpack-plugin');

module.exports = {
    entry: './src/index.jsx',
    output: {
        filename: 'bundle.js',
        path: path.resolve(__dirname, 'dist')
    },
    module: {
        rules: [
          {
            test: /\.m?jsx?$/,
            exclude: /(node_modules|bower_components)/,
            use: {
              loader: 'babel-loader',
              options: {
                presets: ['@babel/preset-env', '@babel/preset-react']
              }
            }
          }
        ]
    },
    plugins: [new HtmlWebpackPlugin()],
    devServer: {
        contentBase: path.join(__dirname, 'dist'),
        compress: true,
        port: 9000,
      },
}

package.json:

{
  "name": "first-react",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "dev": "webpack serve --mode development",
    "build": "webpack --mode development"
  },
  "browserslist": "> 0.25%, not dead",
  "repository": {
    "type": "git",
    "url": "git+https://github.com/Marat20/First-React.git"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "bugs": {
    "url": "https://github.com/Marat20/First-React/issues"
  },
  "homepage": "https://github.com/Marat20/First-React#readme",
  "devDependencies": {
    "@babel/core": "^7.14.3",
    "@babel/preset-env": "^7.14.2",
    "@babel/preset-react": "^7.13.13",
    "babel-loader": "^8.2.2",
    "html-webpack-plugin": "^5.3.1",
    "webpack": "^5.37.1",
    "webpack-cli": "^4.7.0",
    "webpack-dev-server": "^3.11.2"
  },
  "dependencies": {
    "react": "^17.0.2",
    "react-dom": "^17.0.2"
  }
}

Answer 1

let block = document.querySelector('#app')
In this line, you are trying to access an element with id=#app that you don't see.

Answer 2

Who will have a similar problem, pay attention in webpack.config to:

plugins: [
        new HtmlWebpackPlugin({
            title: './index.html'
        })
    ],

To ensure that the path to your html file is correct.
This error is present when template : './index.html' is replaced by title : 'Some title'