getEnforcedCardinality example

'#type' => 'fieldset',
      '#title' => $this->t('Allowed number of values'),
      '#attributes' => [
        'class' => [
          'container-inline',
          'fieldgroup',
          'form-composite',
        ],
      ],
    ];

    if ($enforced_cardinality = $this->getEnforcedCardinality()) {
      if ($enforced_cardinality === FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED) {
        $markup = $this->t("This field cardinality is set to unlimited and cannot be configured.");
      }
      else {
        $markup = $this->t("This field cardinality is set to @cardinality and cannot be configured.", ['@cardinality' => $enforced_cardinality]);
      }
      $form['cardinality'] = ['#markup' => $markup];
    }
    else {
      $form['#element_validate'][] = '::validateCardinality';
      $cardinality = $this->entity->getCardinality();