When you saw the new features listed on the official blog:

• useTransition: Just startTransition with pending state.
• useActionState: useTransition + useState
• Form action as function: VS react-hook-form
• useFormStatus: useContext(<form>)
• useOptimistic: HERE COMES A NEW CHALLENGER!
• use: React.lazy without dynamic import + @tanstack/query
• Server component and Server Action: for SSR Only
• ref as Prop: Yes. you can cleanup as callback ref. This feature has made other JS libraries more friendly, making it worth competing with other frontend tech stacks.
• Hydration error: for SSR Only 2
• Context is Provider by default: The beginning of the end for class components.
• <Suspense> waterfall issue: RESOLVED!
• <meta>, <link>, <script async>, <custom-element>: so what?

Recap

You are ready and good to upgrade!

• Next.js with App Router
• Any integrations with node.js backend server (e.g. express, hono, NestJS, etc.)

No, it's not worth upgrading...

• Any SPA stack
• Full stack framework other than Next.js (Pages router included)
• Any SSG or based framework (e.g. Getsby, Docusaurus, Astro...)
• React Native
• A stack that contains non-webpack bundlers. (yes. Vite.)

Conclusion

This version of React is a major update with the main goal of enhancing server functionality. So you don't need to get excited, and you don't need to upgrade quickly—just keep your version in your existing environment. React is meant to be a library like that. such as Java...