title: Typescript 4 nullish assignment (??=) not working in new CRA project
body: <p>Typescript 4 supports <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_nullish_assignment" rel="nofollow noreferrer">nullish assignment (??=)</a>. CRA 4 released yesterday says it supports TS 4. That operator works in the code editor, but when running <code>yarn start</code> I get:</p>
  <pre><code>Module parse failed: Unexpected token (14:10)
  File was processed with these loaders:
   * ./node_modules/@pmmmwh/react-refresh-webpack-plugin/loader/index.js  
   * ./node_modules/babel-loader/lib/index.js
  You may need an additional loader to handle the result of these loaders.
  </code></pre>
  <p>To reproduce the problem I just create a new app with CRA with Typescript support. Then just add the following lines to App.tsx:</p>
  <pre><code>const test = { a: 1 };
  test.a ??= 2;
  </code></pre>
  <p>Any ideas? I don't know much about Babel/Webpack.</p>