put the DatePicker in a form with a reset button and assign an inputName:

export function PickerExample() {
  return (
    <form>
      <DatePicker inputName={'_in'} value={null} onChange={_ => {}}/>
      <button type=reset">Reset</button>
    </form>
  )
}

Select a date, then press the reset button...
Normally a reset event should trigger a form elements collection to adopt the reset mechanism, by emptying themselves.
Although the DatePicker component includes a element, this won't be cleared.

It should either expose a .Reset() function to be invoked via the useRef() hook, or it should be fixed to use the form events as intended.