diff --git a/core/modules/layout_builder/src/Form/LayoutBuilderEntityViewDisplayForm.php b/core/modules/layout_builder/src/Form/LayoutBuilderEntityViewDisplayForm.php
index 12049f55c6..5b299ecaa1 100644
--- a/core/modules/layout_builder/src/Form/LayoutBuilderEntityViewDisplayForm.php
+++ b/core/modules/layout_builder/src/Form/LayoutBuilderEntityViewDisplayForm.php
@@ -83,7 +83,7 @@ public function form(array $form, FormStateInterface $form_state) {
 
     // @todo Expand to work for all view modes in
     //   https://www.drupal.org/node/2907413.
-    if ($this->entity->getMode() === 'default') {
+    if ($this->isCanonicalMode($this->entity->getMode())) {
       $entity_type = $this->entityTypeManager->getDefinition($this->entity->getTargetEntityTypeId());
       $form['layout']['allow_custom'] = [
         '#type' => 'checkbox',
@@ -113,9 +113,45 @@ public function form(array $form, FormStateInterface $form_state) {
         unset($form['#entity_builders']['layout_builder']);
       }
     }
+    // For non-canonical modes, the existing value should be preserved.
+    else {
+      $form['layout']['allow_custom'] = [
+        '#type' => 'value',
+        '#value' => $this->entity->isOverridable(),
+      ];
+    }
     return $form;
   }
 
+  /**
+   * Determines if the mode is used by the canonical route.
+   *
+   * @param string $mode
+   *   The view mode.
+   *
+   * @return bool
+   *   TRUE if the mode is valid, FALSE otherwise.
+   */
+  protected function isCanonicalMode($mode) {
+    // @todo This is a convention core uses but is not a given, nor is it easily
+    //   introspectable. Address in https://www.drupal.org/node/2907413.
+    $canonical_mode = 'full';
+
+    if ($mode === $canonical_mode) {
+      return TRUE;
+    }
+
+    // The default mode is valid if the canonical mode is not enabled.
+    if ($mode === 'default') {
+      $query = $this->entityTypeManager->getStorage($this->entity->getEntityTypeId())->getQuery()
+        ->condition('status', TRUE)
+        ->condition('mode', $canonical_mode);
+      return !$query->count()->execute();
+    }
+
+    return FALSE;
+  }
+
   /**
    * Determines if the defaults have any overrides.
    *
diff --git a/core/modules/layout_builder/tests/src/Functional/LayoutBuilderTest.php b/core/modules/layout_builder/tests/src/Functional/LayoutBuilderTest.php
index 5629dc9982..d54180978b 100644
--- a/core/modules/layout_builder/tests/src/Functional/LayoutBuilderTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/LayoutBuilderTest.php
@@ -580,6 +580,12 @@ public function testLayoutBuilderUiFullViewMode() {
     ]));
 
     $field_ui_prefix = 'admin/structure/types/manage/bundle_with_section_field';
+
+    // For the purposes of this test, turn the full view mode on and off to
+    // prevent copying from the customized default view mode.
+    $this->drupalPostForm("$field_ui_prefix/display/default", ['display_modes_custom[full]' => TRUE], 'Save');
+    $this->drupalPostForm("$field_ui_prefix/display/default", ['display_modes_custom[full]' => FALSE], 'Save');
+
     // Allow overrides for the layout.
     $this->drupalPostForm("$field_ui_prefix/display/default", ['layout[enabled]' => TRUE], 'Save');
     $this->drupalPostForm("$field_ui_prefix/display/default", ['layout[allow_custom]' => TRUE], 'Save');
@@ -597,14 +603,17 @@ public function testLayoutBuilderUiFullViewMode() {
     // The default view mode is used for both the node display and layout UI.
     $this->drupalGet('node/1');
     $assert_session->pageTextContains('This is the default view mode');
+    $assert_session->pageTextNotContains('This is the full view mode');
     $this->drupalGet('node/1/layout');
     $assert_session->pageTextContains('This is the default view mode');
+    $assert_session->pageTextNotContains('This is the full view mode');
     $page->pressButton('Discard changes');
     $page->pressButton('Confirm');
 
     // Enable the full view mode and customize it.
     $this->drupalPostForm("$field_ui_prefix/display/default", ['display_modes_custom[full]' => TRUE], 'Save');
     $this->drupalPostForm("$field_ui_prefix/display/full", ['layout[enabled]' => TRUE], 'Save');
+    $this->drupalPostForm("$field_ui_prefix/display/full", ['layout[allow_custom]' => TRUE], 'Save');
     $this->drupalGet("$field_ui_prefix/display/full/layout");
     $this->clickLink('Add Block');
     $this->clickLink('Powered by Drupal');
@@ -617,8 +626,10 @@ public function testLayoutBuilderUiFullViewMode() {
     // The full view mode is now used for both the node display and layout UI.
     $this->drupalGet('node/1');
     $assert_session->pageTextContains('This is the full view mode');
+    $assert_session->pageTextNotContains('This is the default view mode');
     $this->drupalGet('node/1/layout');
     $assert_session->pageTextContains('This is the full view mode');
+    $assert_session->pageTextNotContains('This is the default view mode');
     $page->pressButton('Discard changes');
     $page->pressButton('Confirm');
 
@@ -626,8 +637,97 @@ public function testLayoutBuilderUiFullViewMode() {
     $this->drupalPostForm("$field_ui_prefix/display/default", ['display_modes_custom[full]' => FALSE], 'Save');
     $this->drupalGet('node/1');
     $assert_session->pageTextContains('This is the default view mode');
+    $assert_session->pageTextNotContains('This is the full view mode');
     $this->drupalGet('node/1/layout');
     $assert_session->pageTextContains('This is the default view mode');
+    $assert_session->pageTextNotContains('This is the full view mode');
+    $page->pressButton('Discard changes');
+    $page->pressButton('Confirm');
+
+    // Re-enabling the full view mode restores the layout changes.
+    $this->drupalPostForm("$field_ui_prefix/display/default", ['display_modes_custom[full]' => TRUE], 'Save');
+    $this->drupalGet('node/1');
+    $assert_session->pageTextContains('This is the full view mode');
+    $assert_session->pageTextNotContains('This is the default view mode');
+    $this->drupalGet('node/1/layout');
+    $assert_session->pageTextContains('This is the full view mode');
+    $assert_session->pageTextNotContains('This is the default view mode');
+
+    // Create an override of the full view mode.
+    $this->clickLink('Add Block');
+    $this->clickLink('Powered by Drupal');
+    $page->fillField('settings[label]', 'This is an override of the full view mode');
+    $page->checkField('settings[label_display]');
+    $page->pressButton('Add Block');
+    $assert_session->pageTextContains('This is an override of the full view mode');
+    $page->pressButton('Save layout');
+
+    $this->drupalGet('node/1');
+    $assert_session->pageTextContains('This is the full view mode');
+    $assert_session->pageTextContains('This is an override of the full view mode');
+    $assert_session->pageTextNotContains('This is the default view mode');
+    $this->drupalGet('node/1/layout');
+    $assert_session->pageTextContains('This is the full view mode');
+    $assert_session->pageTextContains('This is an override of the full view mode');
+    $assert_session->pageTextNotContains('This is the default view mode');
+    $page->pressButton('Discard changes');
+    $page->pressButton('Confirm');
+
+    // The override does not affect the full view mode.
+    $this->drupalGet("$field_ui_prefix/display/full/layout");
+    $assert_session->pageTextContains('This is the full view mode');
+    $assert_session->pageTextNotContains('This is an override of the full view mode');
+    $assert_session->pageTextNotContains('This is the default view mode');
+
+    // Reverting the override restores back to the full view mode.
+    $this->drupalGet('node/1/layout');
+    $page->pressButton('Revert to default');
+    $page->pressButton('Revert');
+    $assert_session->pageTextContains('This is the full view mode');
+    $assert_session->pageTextNotContains('This is an override of the full view mode');
+    $assert_session->pageTextNotContains('This is the default view mode');
+    $this->drupalGet('node/1/layout');
+    $assert_session->pageTextContains('This is the full view mode');
+    $assert_session->pageTextNotContains('This is an override of the full view mode');
+    $assert_session->pageTextNotContains('This is the default view mode');
+
+    // Recreate an override of the full view mode.
+    $this->clickLink('Add Block');
+    $this->clickLink('Powered by Drupal');
+    $page->fillField('settings[label]', 'This is an override of the full view mode');
+    $page->checkField('settings[label_display]');
+    $page->pressButton('Add Block');
+    $assert_session->pageTextContains('This is an override of the full view mode');
+    $page->pressButton('Save layout');
+
+    $assert_session->pageTextContains('This is the full view mode');
+    $assert_session->pageTextContains('This is an override of the full view mode');
+    $assert_session->pageTextNotContains('This is the default view mode');
+    $this->drupalGet('node/1/layout');
+    $assert_session->pageTextContains('This is the full view mode');
+    $assert_session->pageTextContains('This is an override of the full view mode');
+    $assert_session->pageTextNotContains('This is the default view mode');
+    $page->pressButton('Discard changes');
+    $page->pressButton('Confirm');
+
+    // Disable the full view mode.
+    $this->drupalPostForm("$field_ui_prefix/display/default", ['display_modes_custom[full]' => FALSE], 'Save');
+
+    // The override of the full view mode is still available.
+    $this->drupalGet('node/1');
+    $assert_session->pageTextContains('This is the full view mode');
+    $assert_session->pageTextContains('This is an override of the full view mode');
+    $assert_session->pageTextNotContains('This is the default view mode');
+
+    // Reverting the override restores back to the default view mode.
+    $this->drupalGet('node/1/layout');
+    $page->pressButton('Revert to default');
+    $page->pressButton('Revert');
+    $assert_session->pageTextContains('This is the default view mode');
+    $assert_session->pageTextNotContains('This is the full view mode');
+    $this->drupalGet('node/1/layout');
+    $assert_session->pageTextContains('This is the default view mode');
+    $assert_session->pageTextNotContains('This is the full view mode');
     $page->pressButton('Discard changes');
     $page->pressButton('Confirm');
   }