[docs] Activity chooser core_courseformat

Author: ferranrecio

docs/devupdate.md

@@ -19,9 +19,32 @@ Most Moodle tooling has already been updated to support this, but minor web serv
 
 See the [Restructure documentation](./guides/restructure/index.md) for further information on some of the changes required.
 
-## Course: activity chooser footer has been changed
+## Course format: activity chooser is now in core_courseformat
 
 <Since version="5.1" issueNumber="MDL-85597" />
+The activity chooser logic and templates have been relocated from `core_course` to `core_courseformat`. This change may impact themes that override the activity chooser rendering, but it also enables format plugins to provide custom outputs and templates for activity chooser elements, similar to other course content components. For details on how format can override outputs, see the [overriding output classes from course format plugin page](http://localhost:3000/docs/5.1/apis/plugintypes/format#override-output-classes).s
+
+**How to check if your plugin is affected:**
+
+For theme plugins, review whether any of the following templates are overridden:
+
+- `core_course/activitychooser` (now in `core_courseformat/activitychooser`)
+- `core_course/activitychooserbutton` (now in `core_courseformat/local/content/activitychooserbutton`)
+- Any template in `core_course/local/activitychooser` (now in `core_courseformat/local/activitychooser`)
+
+Additionally, renderer methods for loading the activity chooser have changed. Check if your format or theme overrides the following method:
+
+- `core_course_renderer::course_activitychooser` (no longer used)
+
+**What you need to do:**
+
+- Move any overridden templates or AMD modules to their new locations in `core_courseformat`.
+- Follow any deprecation notices for the activity chooser.
+
+## Course format: activity chooser footer has been changed
+
+<Since version="5.1" issueNumber="MDL-85597" />
+
 The activity chooser UI now features a dedicated footer button for adding the selected activity to the course. The logic for managing the activity chooser footer has moved to `course/amd/src/local/activitychooser/dialogue.js`, which now controls the visibility of the back and add buttons based on the modal's content. This update may impact plugins that implement custom activity chooser footers.
 
 **How to determine if your plugin is affected:**