Not too familiar with React server components, so I have a question.

Are you implying that a client rendered component can be different from a server rendered one? I always assumed this was just implementation details for the same result.

They can be different in that server rendered ones are materialized solely on the server, without any context to the browser environment and unable to have any interactivity. It's just HTML when it's SSR'd. However, when "hydrated" or when that component is rendered on the client (browser), it can ship with more interactivity and/or manipulation by its JS.

I saw a company using it with their homemade php backend/components.