That's not true, though; JSX can be entirely prerendered server-side. If you don't write client-side JavaScript, you're not going to get client-side JavaScript

That's not true, though; JSX can be entirely prerendered server-side. If you don't write client-side JavaScript, you're not going to get client-side JavaScript (modulo maybe a thin hydration layer if you're using particularly old tools, but nothing running pervasively). Your code becomes HTML files. It's more Hugo/Jekyll than it is "a SPA". I am unaware of a major PHP framework that is designed around similar, though it may exist.