Patch to bring feature allowing to export config split configurations.

config_split-config-export.patch

diff --git a/config_split.module b/config_split.module
index 0cd7135..adcbb4b 100644
--- a/config_split.module
+++ b/config_split.module
@@ -9,6 +9,8 @@
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Link;
 use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\StreamWrapper\StreamWrapperManager;
+use Drupal\config_split\Controller\ConfigDownloadController;
 
 /**
  * Implements hook_form_FORM_ID_alter().
@@ -127,3 +129,20 @@ function config_split_config_readonly_whitelist_patterns() {
   }
   return $patterns;
 }
+
+/**
+ * Implements hook_file_download().
+ */
+function  config_split_file_download($uri) {
+  $scheme = StreamWrapperManager::getScheme($uri);
+  $target = StreamWrapperManager::getTarget($uri);
+  if ($scheme == 'temporary' && str_starts_with($target, ConfigDownloadController::FILE_PREFIX)) {
+    if (\Drupal::currentUser()->hasPermission('administer configuration split')) {
+      $disposition = 'attachment; filename="' . $target . '"';
+      return [
+        'Content-disposition' => $disposition,
+      ];
+    }
+    return -1;
+  }
+}
diff --git a/config_split.routing.yml b/config_split.routing.yml
index 604a8a8..2d212b3 100644
--- a/config_split.routing.yml
+++ b/config_split.routing.yml
@@ -65,3 +65,11 @@ config_split.diff_collection:
     target_name: NULL
   requirements:
     _permission: 'administer configuration split'
+
+config_split.entity_export_download:
+  path: '/admin/config/development/configuration/config-split/{config_split}/download'
+  defaults:
+    _controller: '\Drupal\config_split\Controller\ConfigDownloadController::download'
+    _title: 'Download'
+  requirements:
+    _permission: 'administer configuration split'
diff --git a/src/Controller/ConfigDownloadController.php b/src/Controller/ConfigDownloadController.php
new file mode 100644
index 0000000..ebdce8e
--- /dev/null
+++ b/src/Controller/ConfigDownloadController.php
@@ -0,0 +1,108 @@
+<?php
+
+namespace Drupal\config_split\Controller;
+
+use Symfony\Component\HttpFoundation\Request;
+use Drupal\system\FileDownloadController;
+use Drupal\Core\Archiver\ArchiveTar;
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Drupal\Core\State\StateInterface;
+use Drupal\config_split\ConfigSplitManager;
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\Serialization\Yaml;
+
+class ConfigDownloadController implements ContainerInjectionInterface {
+
+  const FILE_PREFIX = 'config-split--';
+
+  /**
+   * The state keyvalue collection.
+   *
+   * @var \Drupal\Core\State\StateInterface
+   */
+  protected $state;
+
+  /**
+   * The split manager.
+   *
+   * @var \Drupal\config_split\ConfigSplitManager
+   */
+  protected $manager;
+  
+  /**
+   * @var \Drupal\Core\Routing\RouteMatchInterface
+   */
+  protected $routeMatch;
+
+  /**
+   * The constructor.
+   *
+   * @param \Drupal\Core\Config\StorageInterface $activeStorage
+   *   The active storage.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entityTypeManager
+   *   The entity type manager.
+   * @param \Drupal\Core\Config\ConfigManagerInterface $configManager
+   *   The config manager.
+   * @param \Drupal\Core\Diff\DiffFormatter $diffFormatter
+   *   The diff formatter.
+   * @param \Drupal\config_split\ConfigSplitManager $configSplitManager
+   *   The split manager.
+   */
+  public function __construct(StateInterface $state, ConfigSplitManager $configSplitManager, RouteMatchInterface $route_match) {
+    $this->state = $state;
+    $this->manager = $configSplitManager;
+    $this->routeMatch = $route_match;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('state'),
+      $container->get('config_split.manager'),
+      $container->get('current_route_match')
+    );
+  }
+
+  /**
+   * Get a split from the route.
+   *
+   * @return \Drupal\Core\Config\ImmutableConfig
+   *   The split config.
+   */
+  protected function getSplit() {
+    $split = $this->manager->getSplitConfig($this->routeMatch->getRawParameter('config_split'));
+    if ($split === NULL) {
+      throw new \UnexpectedValueException("Unknown split");
+    }
+    return $split;
+  }
+
+  public function download() {
+    $request = \Drupal::request();
+    $file_system = \Drupal::service('file_system');
+    $split = $this->getSplit();
+
+    $date = \DateTime::createFromFormat('U', $request->server->get('REQUEST_TIME'));
+    $date_string = $date->format('Y-m-d-H-i');
+
+    $filename = self::FILE_PREFIX . $split->get('id') . '-' . $date_string . '.tar.gz';
+
+    $archiver = new ArchiveTar($file_system->getTempDirectory() . '/' . $filename, 'gz');
+
+    $target = $this->manager->singleExportTarget($split);
+
+    $names = $target->listAll();
+    foreach ($names as $name) {
+      $archiver->addString($name . '.yml', Yaml::encode($target->read($name)));
+    }
+
+    $request = new Request(['file' => $filename]);
+
+    $file_download_controller = new FileDownloadController(\Drupal::service('stream_wrapper_manager'));
+
+    return $file_download_controller->download($request, 'temporary');
+  }
+}
\ No newline at end of file
diff --git a/src/Form/ConfigImportFormTrait.php b/src/Form/ConfigImportFormTrait.php
index 258dc51..add1eca 100644
--- a/src/Form/ConfigImportFormTrait.php
+++ b/src/Form/ConfigImportFormTrait.php
@@ -98,6 +98,11 @@ protected function buildFormWithStorageComparer(
         '#empty' => $this->t('There are no configuration changes to make.'),
       ];
       $form['actions']['#access'] = FALSE;
+      $form['download'] = [
+        '#title' => $this->t('Download'),
+        '#type' => 'link',
+        '#url' => Url::fromRoute('config_split.entity_export_download', ['config_split' => $options['route']['config_split']]),
+      ];
       return $form;
     }
     elseif ($validate && !$storage_comparer->validateSiteUuid()) {