In my case, I'm trying to add Jest for unit testing. Jest needs to transpile the unit test code to ES5 before running it, because there're some ESNext syntax node.js does not understand, such as nullish assignment operator ?=.

However, I'm sure there're tons of other scenarios adding @babel/preset-env is necessary, so it's impactful to have this bug fixed.

Step 1) yarn add @babel/preset-env

Step 2) Add to package.json:

"babel": {
    "presets": [
      "@babel/preset-env"
    ]
 },

Result:
Launch website at http://localhost:3000, the webpage crashes, logging error in the browser: Uncaught SyntaxError: The requested module '/src/App.jsx' does not provide an export named 'default'

Why does adding this cause such an error? How can I fix this?