Class components still work, and you can still use function components with hooks inside class components and vice versa.

In the parent comment's case of not having other dependencies, whatever the React ecosystem does isn't relevant if you aren't using any React libraries, which aren't really necessary anyways, especially nowadays when the LLM can reimplement what you need for you.

Nothing has changed about react-dom that prevents you from using React piece by piece—its docs still recommend attaching to a #root node even for single page apps.

Including web components in a React app is very seamless, and embedding non-React-controlled elements inside React is not uncommon (e.g. canvas, Monaco, maps), though for common use cases there's usually convenience libraries for React that wrap around these.