isAuth is not defined

i defined isAuth in Line 14 but i got error "src\App.js Line 25:13: 'isAuth' is not defined no-undef" idk, maybe i defined it wrong, looking up for your help, thanks

import React, { Component } from 'react';
import './css/main.css';
import { BrowserRouter as Router, Routes, Route, Link } from 'react-router-dom';
import Home from './pages/Home';
import CreatePost from './pages/CreatePost';
import Login from './pages/Login';


class App extends Component {

  constructor(props) {
    super(props);
    this.state = {
      isAuth: false,
      setIsAuth: false
    };
  }

  render() {
    return (
      <Router>
        <nav>
          <Link to="/">Home</Link>
          <Link to="/createpost"> Create New Post</Link>
          {!isAuth && <Link to="/login">Login</Link>}
        </nav>
        <Routes>
          <Route path="/" element={<Home />} />
          <Route path="/login" element={<Login setIsAuth={this.state.setIsAuth} />} />
          <Route path="/createpost" element={<CreatePost />} />
        </Routes>
      </Router>
    );
  }
}

export default App;

To access a property of the state, you need to add this.state.

like this :

{!this.state.isAuth

or this :

render() {
    const { isAuth } = this.state;
    return (