Edit – I think I found it: RSC is React Server Components. Per React’s December 2020 blog post https://reactjs.org/blog/2020/12/21/data-fetching-with-react... and June 2022 blog post https://reactjs.org/blog/2022/06/15/react-labs-what-we-have-..., the technology is still in development.
Searches like “RSC JavaScript” and “RSC Redux” didn’t turn up anything. I only found the term “React Server Components” in the comment https://news.ycombinator.com/item?id=29994621 while reading discussion of a January 2022 blog post “Remix vs Next.js”.
