You still can't add features like error boundaries in React without class-based components somewhere in your app. Even if they added these features to functional components today, it would be years before they'd consider them safe to remove.
HOC still exist and builtin features like `React.memo(MyComponent)` along with the like of more functional styles means they aren't ever going away.
But they're not deprecated. Where's the forced churn?
Every place that I've been at has made the gradual shift to migrate stuff away from class components as new stuff gets built or refactored. Seems like a pretty common development habit.
Mea culpa: they’re not being deprecated. But the existence of custom hooks removes the bulk of (if not all of) their utility, and make it much easier to reason about code and make your code well-typed.