⚠️ **Subject.create:** Removed the deprecated `Subject.create` method. ([d62ce6ebe](https://github.com/ReactiveX/rxjs/commit/d62ce6ebe))
⚠️ **WebSocketSubject:** no longer extends `Subject`. ([54f2f6ed1](https://github.com/ReactiveX/rxjs/commit/54f2f6ed1))
fromEvent:** passing a generic parameter is no longer deprecated ([#7406](https://github.com/ReactiveX/rxjs/pull/7406))
⚠️ Breaking Changes
observable (Symbol):** `observable` (the `Symbol.observable` symbol instance) is no longer exported. Use a polyfill like `symbol-observable`, or use `Symbol.observable ?? '@@observable'` as a workaround."
WebSocketSubject:** `WebSocketSubject` is no longer `instanceof Subject`. Check for `instanceof WebSocketSubject` instead.