docs: clarify app.setName() effects (#19893)

* Document that `app.setName()` has no effect in Mac environments

* docs: add note to clarify `app.setName()` functionality

* Update app.md

docs/api/app.md

@@ -675,6 +675,8 @@ preferred over `name` by Electron.
 
 Overrides the current application's name.
 
+**Note:** This function overrides the name used internally by Electron; it does not affect the name that the OS uses.
+
 **[Deprecated](modernization/property-updates.md)**
 
 ### `app.getLocale()`