If we're calling both "framework" (though as another commenter mentioned, the React package is pretty much just a UI library) then you can think of React as a UI framework and Remix as an application framework. You use the React UI framework in the Remix (or NextJS) application framework.
People are using the term “metaframework” these days to describe things like Remix and Next that build on top of React as the view layer and provide many of the other bits you might need to get a fully-fledged web app up and running. Including but not limited to routing, performance optimizations for images and fonts, data fetching, SSR/static generation & regeneration
The main differentiator between the two is Inversion of Control.
React developers write their code to be called by the React application. You aren't choosing to include React or not (what you would do with a library), your whole frontend application is built within the context of the React environment in which it will run.
That sounds nice but it’s not that simple. In the case of react you are doing both. You are importing functions like hooks and render. Then you pass render a function that then gets called by react.