diff --git a/developer_manual/app_publishing_maintenance/upgrade-guide.rst b/developer_manual/app_publishing_maintenance/upgrade-guide.rst
index 4334bb845..c92e825a5 100644
--- a/developer_manual/app_publishing_maintenance/upgrade-guide.rst
+++ b/developer_manual/app_publishing_maintenance/upgrade-guide.rst
@@ -6,6 +6,30 @@ Once you've created and published the first version of your app, you will want t
 
 This document will cover the most important changes in Nextcloud, as well as some guides on how to upgrade existing apps.
 
+Upgrading to Nextcloud 23
+-------------------------
+
+.. note:: Critical changes were collected `on GitHub <https://github.com/nextcloud/server/issues/27846>`__. See the original ticket for links to the pull requests and tickets.
+
+Back-end changes
+^^^^^^^^^^^^^^^^
+
+Changed APIs
+************
+
+* ``\OCP\User\Events\UserLoggedInEvent::getPassword`` is now nullable because logins are possible without a password in SSO setups
+
+Deprecated APIs
+***************
+
+* ``\OCP\Calendar\IManager::search``: use :ref:`the new calendar search API<calendar-search>`
+* ``\OCP\Calendar\IManager::isEnabled``: there is no replacement
+* ``\OCP\Calendar\IManager::registerCalendar``: use :ref:`calendar providers<calendar-providers>`
+* ``\OCP\Calendar\IManager::unregisterCalendar`` there is no replacement
+* ``\OCP\Calendar\IManager::register``: use :ref:`calendar providers<calendar-providers>`
+* ``\OCP\Calendar\IManager::getCalendars``: use :ref:`the new calendar API<calendar-access>`
+* ``\OCP\Calendar\IManager::clear``: there is no replacement
+
 Upgrading to Nextcloud 22
 -------------------------
 
diff --git a/developer_manual/digging_deeper/groupware/calendar.rst b/developer_manual/digging_deeper/groupware/calendar.rst
index 2f7df3d41..91467c837 100644
--- a/developer_manual/digging_deeper/groupware/calendar.rst
+++ b/developer_manual/digging_deeper/groupware/calendar.rst
@@ -7,6 +7,8 @@ On this page you can learn more about integrating with the Nextcloud calendar se
 Access calendars and events
 ---------------------------
 
+.. _calendar-search:
+
 Calendar objects
 ~~~~~~~~~~~~~~~~
 
@@ -51,6 +53,8 @@ In the following example you see a basic use case of the calendar query API wher
 
 Study the interface ``\OCP\Calendar\ICalendarQuery`` to learn more about other query options.
 
+.. _calendar-access:
+
 Calendars
 ~~~~~~~~~
 
@@ -100,6 +104,8 @@ The returned objects implement ``\OCP\Calendar\ICalendar``. Study the interface
 
 .. note:: All calendars are by default only readable, therefore ``ICalendar`` does not offer methods for mutation. Some of the calendars are mutable, however, and they may further extend the interface ``\OCP\Calendar\ICreateFromString``.
 
+.. _calendar-providers:
+
 Calendar providers
 ------------------