Use field.rel over field.related, rel.model over rel.to

wagtail/wagtailadmin/edit_handlers.py

@@ -484,7 +484,7 @@ class BaseChooserPanel(BaseFieldPanel):
 
     def get_chosen_item(self):
         field = self.instance._meta.get_field(self.field_name)
-        related_model = field.related.model
+        related_model = field.rel.model
         try:
             return getattr(self.instance, self.field_name)
         except related_model.DoesNotExist:

wagtail/wagtailsnippets/edit_handlers.py

@@ -41,7 +41,7 @@ class BaseSnippetChooserPanel(BaseChooserPanel):
                         .format(cls.__name__, cls.snippet_type)
                     )
             else:
-                cls._target_model = cls.model._meta.get_field(cls.field_name).rel.to
+                cls._target_model = cls.model._meta.get_field(cls.field_name).rel.model
 
         return cls._target_model