I fill in the date field behat step definition

step.php

  /**
   * @Then I fill in the date field :field with :date
   *
   * Assign the specified date to the element.
   */
  public function iFillDateField($field, $date): void {
    $field_label = $this->getSession()->getPage()->find('xpath', "//*[text() = '$field']");
    if ($field_label == NULL | !$field_label->hasClass('form-item__label')) {
      throw new ExpectationException('Could not find date field with label: ' . $field, $this->getSession());
    }

    $datetime = new \DateTime($date, \timezone_open('UTC'));
    $datetime->setTimezone(new \DateTimeZone(\date_default_timezone_get()));

    $date_input = $field_label->getParent()->find('xpath', "//input[@type='date']");
    $date_output_string = $datetime->format('Y-m-d');
    $this->getSession()->getPage()->fillField($date_input->getAttribute('id'), $date_output_string);

    $time_input = $field_label->getParent()->find('xpath', "//input[@type='time']");
    if ($time_input) {
      $time_output_string = $datetime->format('H:i:s');
      $this->getSession()->getPage()->fillField($time_input->getAttribute('id'), $time_output_string);
    }
  }