Fix PHP error when merging canonical changes for non-change-tracking

CHANGELOG.md

@@ -11,6 +11,7 @@
 - Fixed a bug where the “All entries” and “All users” sources weren’t available to be selected within Entries/Users field settings. ([#19185](https://github.com/craftcms/cms/discussions/19185))
 - Fixed a bug where database backups weren’t using the `--single-transaction` flag on MariaDB. ([#19191](https://github.com/craftcms/cms/issues/19191))
 - Fixed a bug where element indexes could show multiple table columns for the same nested fields within Content Block fields. ([#19197](https://github.com/craftcms/cms/pull/19197))
+- Fixed a PHP error that could occur when merging canonical changes into a draft that contained nested elements. ([#19187](https://github.com/craftcms/cms/pull/19187))
 
 ## 5.10.8.1 - 2026-06-23
 

src/elements/NestedElementManager.php

@@ -1370,7 +1370,11 @@ private function mergeCanonicalChanges(ElementInterface $owner): void
                         if ($derivativeElement->dateUpdated == $derivativeElement->dateCreated) {
                             $elementsService->deleteElement($derivativeElement);
                         }
-                    } elseif (!$derivativeElement->trashed && ElementHelper::isOutdated($derivativeElement)) {
+                    } elseif (
+                        !$derivativeElement->trashed &&
+                        $derivativeElement::trackChanges() &&
+                        ElementHelper::isOutdated($derivativeElement)
+                    ) {
                         // Merge the upstream changes into the derivative nested element
                         $elementsService->mergeCanonicalChanges($derivativeElement);
                     }