I've created a test react project with the npx create react app and added the electron.js file. I then run the build script and it was compiled successfully but when I try to run the .exe nothing shows and the console returns a Failed to load resource: net::ERR_FILE_NOT_FOUND.

electron.js

const { app, BrowserWindow } = require("electron");
const path = require("path");
const isDev = require("electron-is-dev");

function createWindow() {
  const mainWindow = new BrowserWindow({
    width: 1920,
    height: 1080,
    webPreferences: {
      preload: path.join(__dirname, "preload.js"),
    },
  });

  mainWindow.loadURL(
    isDev
      ? "http://localhost:3000"
      : `file://${path.join(__dirname, "../build/index.html")}`
  );

  mainWindow.webContents.openDevTools();
}

app.whenReady().then(() => {
  createWindow();

  app.on("activate", function () {
    if (BrowserWindow.getAllWindows().length === 0) createWindow();
  });
});

app.on("window-all-closed", function () {
  if (process.platform !== "darwin") app.quit();
});

EDIT: so I tried again from the start and managed to build with just the create-react-app however I've now changed some files with a Routes component and while in dev works fine when I build it nothing shows. console.log are shown but the component isn't.

routes.js

const routes = [
  {
    exact: true,
    path: "/",
    component: lazy(() => import("../test")),
  },
];

const renderRoutes = (routes) =>
  routes ? (
    <Suspense fallback={<div>Loading...</div>}>
      <Switch>
        {routes.map((route, i) => {
          const Layout = route.layout || Fragment;
          const Component = route.component;

          console.log({ Component });

          return (
            <Route
              key={i}
              path={route.path}
              exact
              render={(props) => (
                <Layout>
                  {route.routes ? (
                    renderRoutes(route.routes)
                  ) : (
                    <Component {...props} />
                  )}
                </Layout>
              )}
            />
          );
        })}
      </Switch>
    </Suspense>
  ) : null;

const Routes = () => {
  return renderRoutes(routes);
};

export default Routes;