react.strictmode

<React.StrictMode>
  <div>
    <ComponentOne />
    <ComponentTwo />
  </div>
</React.StrictMode>

// React's StrictMode is sort of a helper component that will help you write better react components, you can wrap a set of components with <StrictMode /> and it'll basically:

// Verify that the components inside are following some of the recommended practices and warn you if not in the console.
// Verify the deprecated methods are not being used, and if they're used strict mode will warn you in the console.
// Help you prevent some side effects by identifying potential risks.
// As the documentation says, strict mode is development oriented so you don't need to worry about it impacting on your production build.

// I've found it especially useful to implement strict mode when I'm working on new code bases and I want to see what kind of code/components I'm facing. Also if you're on bug hunting mode, sometimes it's a good idea to wrap with <StrictMode /> the components/blocks of code you think might be the source of the problem.

// So yeah, you're in the correct path to understanding strict mode, keep it up, I think it's one of those things you understand better when you play with them, so go ahead and have some fun.// https://reactjs.org/docs/strict-mode.html

import React from 'react';

function ExampleApplication() {
  return (
    <div>
      <Header />
      <React.StrictMode>
        <div>
          <ComponentOne />
          <ComponentTwo />
        </div>
      </React.StrictMode>
      <Footer />
    </div>
  );
}

/*
  In the above example, strict mode checks will not be run 
  against the Header and Footer components. 
  However, ComponentOne and ComponentTwo, as well as all of their
  descendants, will have the checks.
*/import React from 'react';

function ExampleApplication() {
  return (
    <div>
      <Header />
      <React.StrictMode>        <div>
          <ComponentOne />
          <ComponentTwo />
        </div>
      </React.StrictMode>      <Footer />
    </div>
  );
}// React.StrictMode should wrap the whole application including the provider too. So Change your code like bellow:  
  <React.StrictMode>
    <Provider store={store}>
      <App />
    </Provider>
  </React.StrictMode>,
  document.getElementById('root')