Earlier quoted context omitted.
I think he means if you want to offer React server side you will need some-sort of web framework to serve it. Usually that's Express or Fastify or something like that.
Next.js does server-rendering and has API routes built-in. No need for Express or Fastify unless you like the DX of those frameworks better.
The parent then asked why do you need to integrate [react] with Express and my answer was if you want to do server side (not using Next)