JSFiddle - React, Tailwind, and code Playground

HTML

<div>
  <span>Etat de la candidature</span>
  <select name="etat">
    <option value="En cours">En cours de traitement</option>
    <option onClick="changeVisibility()" value="Accepté">Accepté</option>
    <option onClick="changeVisibility()" value="Refusé">Refusé</option>
  </select>
</div>
<div id="checkbox" style="visibility: hidden;">
  <span>Envoyer un email automatique </span>
  <input type="checkbox" name="check" id="check"  value="Envoyer un email automatique">
</div>

JavaScript

function hideCheckbox() {
  document.getElementById("checkbox").style.visibility = "hidden";
}

function changeVisibility() {
  document.getElementById("checkbox").style.visibility = "visible";
}