name.theme

<?php 

function name_theme_preprocess_page() {
  // ...

  $variables['social_networks'] = theme_get_setting('social_networks', 'name_theme');
}

name_theme.html.twig

  {% for name, social_network in social_networks %}
    <p>{{ name }}: <br/>
    {{ social_network.url }}
    </p>
  {% endfor %}

theme-settings.php

<?php 

function name_theme_form_system_theme_settings_alter(&$form, \Drupal\Core\Form\FormStateInterface &$form_state, $form_id = NULL)
{

  // ...

  $socialNetworks = theme_get_setting('social_networks', 'name_theme');

  if (!$socialNetworks) {
      $socialNetworks = [
          'facebook' => ['url'=>''],
          'twitter' => ['url'=>''],
          'instagram' => ['url'=>''],
          'youtube' => ['url'=>''],
          'glassdoor' => ['url'=>'']
      ];
  }

    $socialNetworkForm['social_networks'] = [
        '#type' => 'table',
        '#id' => 'draggable-table',
        '#caption' => t('Social Networks.'),
        '#header' => [
            t('Url'),
        ],
        '#tabledrag' => [
            [
                'table_id' => 'draggable-table',
                'action' => 'order',
                'relationship' => 'sibling',
                'group' => 'table-order-weight',
            ],
        ],
    ];

    foreach ($socialNetworks as $name => $socialNetwork) {
        $title = ucfirst(t($name));
        $url = isset($socialNetwork['url'])?$socialNetwork['url']:'';
        $socialNetworkForm['social_networks'][$name] = [
            '#attributes' => ['class' => ['draggable']],
            'url' => [
                '#type' => 'url',
                '#title' => $title,
                '#default_value' => $url,
                '#description' => t("Please provide link of $title"),
            ],
        ];
    }

}