Remove app instances in plugins for layout overrides

migrations/54-60/removed-backward-incompatibility.md

@@ -65,6 +65,19 @@ $article = $app->bootComponent('content')->getMVCFactory()->createModel('Article
 echo $article->title;
 ```
 
+### App variable is removed in plugins
+
+- PR: https://github.com/joomla/joomla-cms/pull/44647
+- Folder: plugins
+- Description: The `$app` variable is left in some plugins for layout overrides of the plugins/tmpl folder and is not used anymore in the plugin class itself and the respective layouts. The `getApplication` function should be used instead  
+```php
+// Old:
+$app = $this->app;
+
+// New:
+$app = $this->getApplication();
+```
+
 ### JCOMPAT_UNICODE_PROPERTIES constant got removed in FormRule class
 
 - PR: https://github.com/joomla/joomla-cms/pull/44662
@@ -77,6 +90,7 @@ echo $article->title;
 - PR: https://github.com/joomla/joomla-cms/pull/44663
 - File: libraries/src/Image/Image.php
 - Description: The `createThumbs` function in the `Image` class got removed as the function `createThumbnails` should be used instead. For example you can use 
+
 ```php
 // Old:
 $image = new Image($path);