docs(dev): remove deprecated createEventSource

Signed-off-by: Daniel Kesselberg <mail@danielkesselberg.de>

Author: kesselb

developer_manual/app_publishing_maintenance/app_upgrade_guide/upgrade_to_28.rst

@@ -45,7 +45,7 @@ Back-end changes
 Added APIs
 ^^^^^^^^^^
 
-* tbd
+* ``\OCP\IEventSourceFactory``: To create a `OCP\IEventSource` instance.
 
 Changed APIs
 ^^^^^^^^^^^^
@@ -66,3 +66,17 @@ Removed APIs
 * ``\OC_App::getSettingsNavigation``: inject ``\OCP\App\IAppManager`` and call ``\OCP\App\IAppManager::getAll('settings')``.
 * ``\OC_App::isEnabled``: inject ``\OCP\App\IAppManager`` and call ``\OCP\App\IAppManager::isEnabledForUser``.
 * ``\OC_Defaults::getLogoClaim``: There is no replacement.
+* `\OC::$server->createEventSource()` has been removed, use `\OC::$server->get(\OCP\IEventSourceFactory::class)->create()` instead. 
+
+The factory `\OCP\IEventSourceFactory` works only from Nextcloud 28. For older versions use \OC::$server->createEventSource().
+
+If you want to support Nextcloud 27 and Nextcloud 28:
+
+.. code-block:: php
+
+// @TODO: Remove method_exists when min-version="28"
+if (method_exists(\OC::$server, 'createEventSource')) {
+	$eventSource = \OC::$server->createEventSource();
+} else {
+	$eventSource = \OCP\Server::get(IEventSourceFactory::class)->create();
+}