Next.js , React, Which is better?

When you want to start an online service, web framework is the most important component. So the most popular framework, React and Next.js based on React, which is the better choice?
We launch an online service https://chillin.online. We developed on React and switch to Next.js, It doesn't mean Next.js is better for all aspects. There are some differences.

React:
Client-Side Rendering (CSR): React applications are CSR, which means the initial rendering happens on the client side, bad for SEO and First Contentful Paint(FCP)
Flexible Route: You can integrate the route in any way without file limit

Next.js:

Less CSS solution: Next.js doesn't support CSS in JS, basically the only CSS solution you can use is Tailwind.
File Route: Just route as the file structure.
More Server needs: It requires the server to render the HTML for each request if you don't use Static Site Generation (SSG), but SSG need more time to build when code has changed.