React state not updated in class

As a backend developer, I am trying to create frontend with React. So, I might have a bit meaningless or simple problem. But I cannot have state updated in the class. However, when I fetch data from backend via axios, inside “render{}” method it gets called.

import "./App.css";
import { Component } from "react";
import { getAllStudents } from "./client";
import Container from "./container";

class App extends Component {
  state = {
    students: [],
    isFetching: false
  };

  fetchStudents = () => {
    this.setState({isFetching  : true});
    getAllStudents()
      .then((res) => res.data)
      .then((students) => {
        console.log(students)
        this.setState({students : students, isFetching: false})
      });
  };

  render() {
    const { students, isFetching } = this.state;

     ...
  }
}

export default App;

An my client:

import axios from "axios";

const instance = axios.create({baseURL: 'http://localhost:8080'})

export const getAllStudents = () => instance.get('/students', {
    timeout: 5000
})

I tried to show data in a table, but it gives an empty array