Cannot clear the value to induce defaultValue

defaultValue is used if initial value is undefined but once value is set to anything then new value becomes the default. I.e. subsequent undefined value will show the value that was previously set.

https://codesandbox.io/s/codesandboxer-example-forked-2j6n7?file=/example.tsx

import React, { Fragment, useState } from "react";
import Select from "react-select";

export default function Example() {
  const options = [
    { label: "zero", value: 0 },
    { label: "one", value: 1 },
    { label: "two", value: 2 }
  ];
  const [value, setValue] = useState(undefined);
  return (
    <Fragment>
      <Select
        defaultValue={options[0]}
        value={value}
        options={options}
        placeholder={"some placeholder"}
        onChange={setValue}
      />
      <button onClick={() => setValue(null)}>Set to null</button>
      <button onClick={() => setValue(undefined)}>Set to undefined</button>
      <button onClick={() => setValue([] as any)}>Set to []</button>
    </Fragment>
  );
}

This example starts with undefined value and correctly shows default of zero.
Change value to "one" then click "Set to undefined" and you will still see "one".
Click "Set to null" and you will get placeholder but click "Set to undefined" and it will be "one" again.

Start with the linked CodeSandbox example and trace how Select handles defaultValue alongside controlled value updates. Reproduce the transitions from an option to undefined, null, and an empty array; done means setting undefined no longer restores the previously selected option while the other demonstrated behaviors remain correct.