Add behavior change in migration guide.

Physics Picking now automatically sets event as handled in Viewports.

tutorials/migrating/upgrading_to_godot_4.1.rst

@@ -202,6 +202,8 @@ Change
 **SubViewportContainer**
 When input events should reach SubViewports and their children, ``SubViewportContainer.mouse_filter`` now needs to be ``MOUSE_FILTER_STOP`` or ``MOUSE_FILTER_PASS``. See `GH-79271`_ for details.  `GH-57894`_
 Multiple layered ``SubViewportContainer`` nodes, that should all receive mouse input events, now need to be replaced by ``Area2D`` nodes. See `GH-79128`_ for details.                              `GH-57894`_
+**Viewport**
+``Viewport`` nodes, that have Physics Picking enabled, now automatically set InputEvents as handled. See `GH-79897`_ for workarounds.                                                               `GH-77595`_
 ==================================================================================================================================================================================================  ===========
 
 
@@ -228,9 +230,11 @@ Multiple layered ``SubViewportContainer`` nodes, that should all receive mouse i
 .. _GH-76688: https://github.com/godotengine/godot/pull/76688
 .. _GH-76794: https://github.com/godotengine/godot/pull/76794
 .. _GH-77143: https://github.com/godotengine/godot/pull/77143
+.. _GH-77595: https://github.com/godotengine/godot/pull/77595
 .. _GH-78237: https://github.com/godotengine/godot/pull/78237
 .. _GH-79128: https://github.com/godotengine/godot/issues/79128
 .. _GH-79271: https://github.com/godotengine/godot/issues/79271
+.. _GH-79897: https://github.com/godotengine/godot/issues/79897
 
 .. _updating_your_gdextension_for_godot_4_1: