Generated product configuration extension not working

[enwikuna]

Hi there, 

the last time I've programmed a Shopify App was 2 years ago. Getting back now and noticed that nearly everything has changed. So I've generated a new App using the latest CLI and generated a custom product configuration extension. When running the dev server and accessing a product, I can not find any entries on a product page. This is the custom generated extension:

import { reactExtension, useApi, Text } from '@shopify/ui-extensions-react/admin';

// The target used here must match the target used in the extension's toml file (./shopify.extension.toml)

export default reactExtension<any>('admin.product-details.configuration.render', () => <App />);

function App() {

  const {extension: {target}, i18n} = useApi<'admin.product-details.configuration.render'>();

  return (
    <Text>
      {i18n.translate('welcome', {target})}
    </Text>
  );
}

It's really just the default one. When checking the console, I can see some errors:

The URL inside the dev console is: https://fears-quickly-admitted-urw.trycloudflare.com/extensions/bb0fbcfa-f823-47aa-bea4-c5a274a5ae24...

I have really no idea how to debug this since the IDE shows no error at all and also the dev console. How would you go on?