diff --git a/core/modules/layout_builder/src/InlineBlockEntityOperations.php b/core/modules/layout_builder/src/InlineBlockEntityOperations.php
index bb709a85cc..a8eafeff8d 100644
--- a/core/modules/layout_builder/src/InlineBlockEntityOperations.php
+++ b/core/modules/layout_builder/src/InlineBlockEntityOperations.php
@@ -59,13 +59,22 @@ class InlineBlockEntityOperations implements ContainerInjectionInterface {
    * @param \Drupal\layout_builder\SectionStorage\SectionStorageManagerInterface $section_storage_manager
    *   The section storage manager.
    * @param \Drupal\Core\Block\BlockManagerInterface|null $block_manager
-   *   The block manager;
+   *   (optional) The block manager;
+   *
+   * @todo This constructor has one optional parameter, $block_manager. Deprecate the current
+   *    constructor signature in https://www.drupal.org/node/3031492 after the
+   *    general policy for constructor backwards compatibility is determined in
+   *    https://www.drupal.org/node/3030640.
    */
-  public function __construct(EntityTypeManagerInterface $entityTypeManager, InlineBlockUsageInterface $usage, SectionStorageManagerInterface $section_storage_manager, BlockManagerInterface $block_manager) {
+  public function __construct(EntityTypeManagerInterface $entityTypeManager, InlineBlockUsageInterface $usage, SectionStorageManagerInterface $section_storage_manager, BlockManagerInterface $block_manager = NULL) {
     $this->entityTypeManager = $entityTypeManager;
     $this->blockContentStorage = $entityTypeManager->getStorage('block_content');
     $this->usage = $usage;
     $this->sectionStorageManager = $section_storage_manager;
+    if ($block_manager === NULL) {
+      @trigger_error('The plugin.manager.block service must be passed to \Drupal\layout_builder\InlineBlockEntityOperations::__construct(). It was added in Drupal 9.1.0 and will be required before Drupal 10.0.0.', E_USER_DEPRECATED);
+      $block_manager = \Drupal::service('plugin.manager.block');
+    }
     $this->blockManager = $block_manager;
   }