diff --git a/core/modules/ckeditor5/src/SmartDefaultSettings.php b/core/modules/ckeditor5/src/SmartDefaultSettings.php
index fe55ab1ad7..b157e11331 100644
--- a/core/modules/ckeditor5/src/SmartDefaultSettings.php
+++ b/core/modules/ckeditor5/src/SmartDefaultSettings.php
@@ -148,11 +148,14 @@ public function computeSmartDefaultSettings(?EditorInterface $text_editor, Filte
     // Compute the appropriate settings based on the CKEditor 4 configuration
     // if it exists.
     $old_editor = $editor->id() ? Editor::load($editor->id()) : NULL;
+    // @todo Remove in https://www.drupal.org/project/drupal/issues/3245351
+    if ($old_editor) {
+      $editor->setImageUploadSettings($old_editor->getImageUploadSettings());
+    }
     $old_editor_restrictions = $old_editor ? HTMLRestrictions::fromTextFormat($old_editor->getFilterFormat()) : HTMLRestrictions::emptySet();
     if ($old_editor && $old_editor->getEditor() === 'ckeditor') {
       [$upgraded_settings, $messages] = $this->createSettingsFromCKEditor4($old_editor->getSettings(), HTMLRestrictions::fromTextFormat($old_editor->getFilterFormat()));
       $editor->setSettings($upgraded_settings);
-      $editor->setImageUploadSettings($old_editor->getImageUploadSettings());
     }
 
     // Add toolbar items based on HTML tags and attributes.
diff --git a/core/modules/ckeditor5/tests/src/FunctionalJavascript/CKEditor5AllowedTagsTest.php b/core/modules/ckeditor5/tests/src/FunctionalJavascript/CKEditor5AllowedTagsTest.php
index 5e7ef0c19c..9462c94405 100644
--- a/core/modules/ckeditor5/tests/src/FunctionalJavascript/CKEditor5AllowedTagsTest.php
+++ b/core/modules/ckeditor5/tests/src/FunctionalJavascript/CKEditor5AllowedTagsTest.php
@@ -22,7 +22,7 @@ class CKEditor5AllowedTagsTest extends CKEditor5TestBase {
    */
   protected static $modules = [
     'node',
-    'ckeditor',
+    'editor_test',
     'ckeditor5',
     'media',
     'media_library',
@@ -37,18 +37,20 @@ class CKEditor5AllowedTagsTest extends CKEditor5TestBase {
   protected $allowedElements = '<br> <p> <h2> <h3> <h4> <h5> <h6> <strong> <em>';
 
   /**
-   * The default allowed elements when updating a non-CKEditor 5 editor.
+   *  The default allowed elements for filter_html's "allowed_html" setting.
+   *
+   * @see \Drupal\filter\Plugin\Filter\FilterHtml
    *
    * @var string
    */
-  protected $defaultElementsWhenUpdatingNotCkeditor5 = '<a href hreflang> <em> <strong> <cite> <blockquote cite> <code> <ul type> <ol start type> <li> <dl> <dt> <dd> <h2 id> <h3 id> <h4 id> <h5 id> <h6 id> <img src alt data-entity-type data-entity-uuid>';
+  protected $defaultElementsWhenUpdatingNotCkeditor5 = "<a href hreflang> <em> <strong> <cite> <blockquote cite> <code> <ul type> <ol start type='1 A I'> <li> <dl> <dt> <dd> <h2 id='jump-*'> <h3 id> <h4 id> <h5 id> <h6 id>";
 
   /**
-   * The expected allowed elements after updating to CKEditor5.
+   * The expected allowed elements after updating to CKEditor 5.
    *
    * @var string
    */
-  protected $defaultElementsAfterUpdatingToCkeditor5 = '<br> <p> <h2 id> <h3 id> <h4 id> <h5 id> <h6 id> <cite> <dl> <dt> <dd> <a hreflang href> <blockquote cite> <ul type> <ol type start> <img src alt data-entity-type data-entity-uuid> <strong> <em> <code> <li>';
+  protected $defaultElementsAfterUpdatingToCkeditor5 = '<br> <p> <h2 id="jump-*"> <h3 id> <h4 id> <h5 id> <h6 id> <cite> <dl> <dt> <dd> <a hreflang href> <blockquote cite> <ul type> <ol type="1 A I" start> <strong> <em> <code> <li>';
 
   /**
    * Test enabling CKEditor 5 in a way that triggers validation.
@@ -60,8 +62,8 @@ public function testEnablingToVersion5Validation() {
     $incompatible_filter_name = 'filters[filter_incompatible][status]';
     $filter_warning = 'CKEditor 5 only works with HTML-based text formats. The "A TYPE_MARKUP_LANGUAGE filter incompatible with CKEditor 5" (filter_incompatible) filter implies this text format is not HTML anymore.';
 
-    $this->createNewTextFormat($page, $assert_session, 'ckeditor');
-    $page->selectFieldOption('editor[editor]', 'ckeditor');
+    $this->createNewTextFormat($page, $assert_session, 'unicorn');
+    $page->selectFieldOption('editor[editor]', 'unicorn');
     $assert_session->assertWaitOnAjaxRequest();
     $page->checkField('filters[filter_html][status]');
     $page->checkField($incompatible_filter_name);
@@ -81,31 +83,16 @@ public function testEnablingToVersion5Validation() {
   }
 
   /**
-   * Tests that when image uploads are enabled in CKEditor 4, they remain in 5.
+   * Tests that when image uploads were enabled, they remain enabled.
    */
   public function testImageUploadsRemainEnabled(): void {
     FilterFormat::create([
-      'format' => 'cke4_image_uploads',
-      'name' => 'CKEditor 4, image uploads',
+      'format' => 'editor_with_image_uploads',
+      'name' => 'Text Editor with image uploads enabled',
     ])->save();
     Editor::create([
-      'format' => 'cke4_image_uploads',
-      'editor' => 'ckeditor',
-      'settings' => [
-        'toolbar' => [
-          'rows' => [
-            0 => [
-              [
-                'name' => 'Media',
-                'items' => [
-                  'DrupalImage',
-                ],
-              ],
-            ],
-          ],
-        ],
-        'plugins' => [],
-      ],
+      'format' => 'editor_with_image_uploads',
+      'editor' => 'unicorn',
       'image_upload' => [
         'status' => TRUE,
         'scheme' => 'public',
@@ -121,14 +108,15 @@ public function testImageUploadsRemainEnabled(): void {
     $page = $this->getSession()->getPage();
     $assert_session = $this->assertSession();
 
-    // Assert that image uploads are enabled initially.
-    $this->drupalGet('admin/config/content/formats/manage/cke4_image_uploads');
-    $this->assertTrue($page->hasCheckedField('Enable image uploads'));
-
     // Switch the text format to CKEditor 5.
+    $this->drupalGet('admin/config/content/formats/manage/editor_with_image_uploads');
     $page->selectFieldOption('editor[editor]', 'ckeditor5');
     $assert_session->assertWaitOnAjaxRequest();
 
+    // Enable the image upload toolbar item.
+    $this->triggerKeyUp('.ckeditor5-toolbar-item-uploadImage', 'ArrowDown');
+    $assert_session->assertWaitOnAjaxRequest();
+
     // Assert that image uploads are still enabled.
     $this->assertTrue($page->hasCheckedField('Enable image uploads'));
   }
@@ -140,7 +128,7 @@ public function testSwitchToVersion5() {
     $page = $this->getSession()->getPage();
     $assert_session = $this->assertSession();
 
-    $this->createNewTextFormat($page, $assert_session, 'ckeditor');
+    $this->createNewTextFormat($page, $assert_session, 'unicorn');
     $assert_session->assertWaitOnAjaxRequest();
 
     // Enable the HTML filter.
@@ -148,15 +136,15 @@ public function testSwitchToVersion5() {
     $page->checkField('filters[filter_html][status]');
     $assert_session->assertWaitOnAjaxRequest();
 
-    // Confirm the allowed HTML tags are the defaults for non-Ckeditor5 editors.
+    // Confirm the allowed HTML tags are the defaults initially.
     $this->assertHtmlEsqueFieldValueEquals('filters[filter_html][settings][allowed_html]', $this->defaultElementsWhenUpdatingNotCkeditor5);
 
     $this->saveNewTextFormat($page, $assert_session);
-    $assert_session->pageTextContains('Added text format ckeditor');
+    $assert_session->pageTextContains('Added text format unicorn');
 
     // Return to the config form to confirm that switching text editors on
     // existing formats will properly switch allowed tags.
-    $this->drupalGet('admin/config/content/formats/manage/ckeditor');
+    $this->drupalGet('admin/config/content/formats/manage/unicorn');
     $assert_session->assertWaitOnAjaxRequest();
     $this->assertHtmlEsqueFieldValueEquals('filters[filter_html][settings][allowed_html]', $this->defaultElementsWhenUpdatingNotCkeditor5);
 
@@ -165,6 +153,14 @@ public function testSwitchToVersion5() {
     $assert_session->pageTextContains('The <br>, <p> tags were added because they are required by CKEditor 5');
     $this->assertHtmlEsqueFieldValueEquals('filters[filter_html][settings][allowed_html]', $this->defaultElementsAfterUpdatingToCkeditor5);
 
+    $page->pressButton('Save configuration');
+    $assert_session->pageTextContains('The text format unicorn has been updated');
+
+    // Return to the confirm form and enable the image upload toolbar item.
+    $this->drupalGet('admin/config/content/formats/manage/unicorn');
+    $this->triggerKeyUp('.ckeditor5-toolbar-item-uploadImage', 'ArrowDown');
+    $assert_session->assertWaitOnAjaxRequest();
+
     $page->pressButton('Save configuration');
 
     $assert_session->pageTextContains('The Image upload toolbar item requires image uploads to be enabled.');
@@ -174,17 +170,7 @@ public function testSwitchToVersion5() {
     $page->checkField('editor[settings][plugins][ckeditor5_imageUpload][status]');
     $assert_session->assertWaitOnAjaxRequest();
     $page->pressButton('Save configuration');
-    $this->assertSession()->pageTextContains('The following attribute(s) are already supported by enabled plugins and should not be added to the Source Editing "Manually editable HTML tags" field: Image (<img src alt data-entity-uuid data-entity-type>)');
-
-    $assert_session->assertWaitOnAjaxRequest();
-    $assert_session->waitForText('Manually editable HTML tags');
-    $source_edit_tags_field = $assert_session->fieldExists('editor[settings][plugins][ckeditor5_sourceEditing][allowed_tags]');
-    $source_edit_tags_field_value = $source_edit_tags_field->getValue();
-    $source_edit_tags_field->setValue(str_replace('<img src alt data-entity-type data-entity-uuid>', '', $source_edit_tags_field_value));
-    $assert_session->assertWaitOnAjaxRequest();
-    $page->pressButton('Save configuration');
-
-    $assert_session->pageTextContains('The text format ckeditor has been updated');
+    $assert_session->pageTextContains('The text format unicorn has been updated');
   }
 
   /**