<label>
  <input type="checkbox" name="options[]" value="other"> Other
</label>
<input type="text" name="otherText" id="otherText" placeholder="Specify other option" style="display: none;">

<script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
<script>
  $(document).ready(function() {
    $('input[name="options[]"]').on('change', function() {
      if ($(this).is(':checked') && $(this).val() === 'other') {
        $('#otherText').show();
      } else {
        $('#otherText').hide();
      }
    });
  });
</script>