I have created a simple component and rendering it in <App> component ie parent component.
In console I see, "Inside simple component" twice.

//App.js

import SimpleComponent from "./SimpleComponent";
export default function App() {
  return <SimpleComponent />;
}

// SimpleComponent.js

  function SimpleComponent() {
   console.log("Inside simple component");
    return <div>Hello world</div>;
  }
  export default SimpleComponent;

Why is it rendering twice?

CodeSandbox for above code.