How extensively is golang used in web?

I'm more familiar with seeing Node.js used as a backend for web applications because Node.js has a richer developer ecosystem for supporting your webapps. Although, that doesn't mean that you can't use Go as a backend for a web application. You can absolutely treat your frontend web app as something that's decoupled from your Go backend.

But, one big benefit of using Node.js as a backend for a React webapp is being able to render React components on the server and serve the rendered pages to the client. You are able to share the same React components on both the frontend and backend.