diff --git a/wagtail/admin/tests/test_workflows.py b/wagtail/admin/tests/test_workflows.py
index 737e9d74d6..09bec53594 100644
--- a/wagtail/admin/tests/test_workflows.py
+++ b/wagtail/admin/tests/test_workflows.py
@@ -3601,11 +3601,35 @@ class TestDashboardWithPages(BasePageWorkflowTests):
             "Compare with previous version",
         )
 
+    def test_dashboard_after_deleting_object_in_moderation(self):
+        # WorkflowState's content_object may point to a nonexistent object
+        # https://github.com/wagtail/wagtail/issues/11300
+        self.login(self.submitter)
+        self.post("submit")
+        self.object.delete()
+
+        response = self.client.get(reverse("wagtailadmin_home"))
+        self.assertEqual(response.status_code, 200)
+        self.assertNotContains(response, "Your pages and snippets in a workflow")
+
+        self.login(self.moderator)
+        response = self.client.get(reverse("wagtailadmin_home"))
+        self.assertEqual(response.status_code, 200)
+        self.assertNotContains(response, "Awaiting your review")
+
 
 class TestDashboardWithSnippets(TestDashboardWithPages, BaseSnippetWorkflowTests):
     pass
 
 
+class TestDashboardWithNonLockableSnippets(TestDashboardWithSnippets):
+    # This model does not use LockableMixin, and it also does not have a
+    # GenericRelation to WorkflowState and Revision, but it should not break
+    # the dashboard.
+    # See https://github.com/wagtail/wagtail/issues/11300 for more details.
+    model = ModeratedModel
+
+
 class TestWorkflowStateEmailNotifier(BasePageWorkflowTests):
     def setUp(self):
         super().setUp()
diff --git a/wagtail/admin/views/home.py b/wagtail/admin/views/home.py
index 0d335bfb65..5829498a75 100644
--- a/wagtail/admin/views/home.py
+++ b/wagtail/admin/views/home.py
@@ -161,6 +161,12 @@ class UserObjectsInWorkflowModerationPanel(Component):
                 )
                 .order_by("-current_task_state__started_at")
             )
+            # Filter out workflow states where the GenericForeignKey points to
+            # a nonexistent object. This can happen if the model does not define
+            # a GenericRelation to WorkflowState and the instance is deleted.
+            context["workflow_states"] = [
+                state for state in context["workflow_states"] if state.content_object
+            ]
         else:
             context["workflow_states"] = WorkflowState.objects.none()
         context["request"] = request
@@ -198,6 +204,12 @@ class WorkflowObjectsToModeratePanel(Component):
         )
         for state in states:
             obj = state.revision.content_object
+            # Skip task states where the revision's GenericForeignKey points to
+            # a nonexistent object. This can happen if the model does not define
+            # a GenericRelation to WorkflowState and/or Revision and the instance
+            # is deleted.
+            if not obj:
+                continue
             actions = state.task.specific.get_actions(obj, request.user)
             workflow_tasks = state.workflow_state.all_tasks_with_status()
 
diff --git a/wagtail/test/testapp/models.py b/wagtail/test/testapp/models.py
index 1636781846..51f88ab3d5 100644
--- a/wagtail/test/testapp/models.py
+++ b/wagtail/test/testapp/models.py
@@ -1123,6 +1123,22 @@ class FullFeaturedSnippet(
 
     some_attribute = "some value"
 
+    workflow_states = GenericRelation(
+        "wagtailcore.WorkflowState",
+        content_type_field="base_content_type",
+        object_id_field="object_id",
+        related_query_name="full_featured_snippet",
+        for_concrete_model=False,
+    )
+
+    revisions = GenericRelation(
+        "wagtailcore.Revision",
+        content_type_field="base_content_type",
+        object_id_field="object_id",
+        related_query_name="full_featured_snippet",
+        for_concrete_model=False,
+    )
+
     search_fields = [
         index.SearchField("text"),
         index.AutocompleteField("text"),