To move CRA application to other directory than src (for example to src/frontend folder)

config-overrides.js

const path = require('path');
const ModuleScopePlugin = require('react-dev-utils/ModuleScopePlugin');

module.exports = {
  paths: function (paths, env) {        
      paths.appIndexJs = path.resolve(__dirname, 'src/frontend/index.js');
      paths.appSrc = path.resolve(__dirname, 'src/frontend');
      return paths;
  },

  override(config, env) {
    config.resolve.plugins = config.resolve.plugins.filter(
      plugin => !(plugin instanceof ModuleScopePlugin)
    );
    return config;
  }
}

install-dependencies.sh

yarn add --dev customize-cra react-app-rewired

package.json

{
  // ...
  "scripts": {
    "start": "react-app-rewired start",
    "build": "react-app-rewired build",
    "test": "react-app-rewired test",
    "eject": "react-app-rewired eject"
  },
  // ...
}