My current company is using a React app, built on top of Create-React-App, and still has some class components sprinkled throughout.
We simply have simply chosen not to rewrite everything each time a shiny new feature comes along. Instead we incrementally adopt the new things as they come along. Everything works fine. Those class components are in parts of the codebase that haven't needed to be updated in years...next time I need to make more than a trivial change to one of those components I'll take the extra 15 minutes to update them to use hooks.
We are looking to get off of CRA since Vite has a much quicker build time - but we've managed to make it ~8 years before deciding this upgrade was worth our time.
We have absolutely 0 plans of migrating to a framework so we can use server components.
The app makes lots and lots of money.