A react framework is a library that is based on react adding other capabilities.
Most of the time, they are web based server framework, adding routing and other web capabilities.
They create a single page application that use a client router and all HTTP must be redirected to it.
Rendering on the server (with node). React - Server Side Rendering (SSR) - DOM Server
This frameworks add Static generation possibility (Each page becomes one HTML page)
The dynamic website is crawled and each page is saved: