React.JS is a library created and maintained by Facebook. It is used to build user interfaces and modern websites, which use API.
React.JS is used on more advanced websites, where the architecture is divided into back-end and front-end.
If you want your app to be well positioned in search results, then Next.JS will be a better solution for you, while keeping all the benefits of using React.JS.
It is a framework, which combines React.JS library, server-side rendering and a few other improvements. Working with Next.JS is only slightly different from React.JS.
Next.JS is better for SEO, because a website is rendered on the server and then sent to the user’s browser, so search engines’ crawlers are able to index content of the website.