All pages are rendered server-side by default. React Server sends each server-side rendered element as soon as it, and every element before it, are ready, up to a timeout, at which point it sends the late arrivals as they trail in. On the client side, React Server picks up where the server left off, to render client side code as the user interacts with the page.

are you asking to have a static site pre-built from React?

I'd assume when he says "first page" he means any first page but generally from there the rest becomes dynamic react. Depending on how you load your data it should be much quicker to render entirely in the browser once the page has loaded.

Well, I was thinking you could have all pages server-side rendered in the case of a low-power mobile device, and leave the hybrid approach for desktop browsers.

The user-agent string could be used to decide which approach to use.

Yep, this is the case