diff --git a/spyder/plugins/outlineexplorer/tests/test_widgets.py b/spyder/plugins/outlineexplorer/tests/test_widgets.py
index 54ab7d741d3..637fe6c5df4 100644
--- a/spyder/plugins/outlineexplorer/tests/test_widgets.py
+++ b/spyder/plugins/outlineexplorer/tests/test_widgets.py
@@ -217,6 +217,37 @@ def test_go_to_last_item(create_outlineexplorer, qtbot):
     assert outlineexplorer.treewidget.currentItem().text(0) == 'method1'
 
 
+@flaky(max_runs=10)
+def test_display_variables(create_outlineexplorer, qtbot):
+    """
+    Test that clicking on the 'Display variables and attributes' button located in the
+    toolbar of the outline explorer is working as expected by updating the tree widget.
+
+    Regression test for spyder-ide/spyder#21456.
+    """
+    outlineexplorer, _ = create_outlineexplorer('text')
+
+    editor = outlineexplorer.treewidget.current_editor
+    state = outlineexplorer.treewidget.display_variables
+
+    editor_id = editor.get_id()
+
+    initial_tree = outlineexplorer.treewidget.editor_tree_cache[editor_id]
+
+    outlineexplorer.treewidget.toggle_variables(not state)
+
+    first_toggle_tree = outlineexplorer.treewidget.editor_tree_cache[editor_id]
+
+    assert first_toggle_tree != initial_tree
+
+    outlineexplorer.treewidget.toggle_variables(state)
+
+    second_toggle_tree = outlineexplorer.treewidget.editor_tree_cache[editor_id]
+
+    assert (second_toggle_tree != first_toggle_tree) and (
+        second_toggle_tree == initial_tree)
+
+
 if __name__ == "__main__":
     import os
     pytest.main(['-x', os.path.basename(__file__), '-v', '-rw'])
diff --git a/spyder/plugins/outlineexplorer/widgets.py b/spyder/plugins/outlineexplorer/widgets.py
index 925779412e4..d31fb682a2d 100644
--- a/spyder/plugins/outlineexplorer/widgets.py
+++ b/spyder/plugins/outlineexplorer/widgets.py
@@ -608,8 +608,7 @@ def update_tree(self, items, editor):
         if not must_update:
             # Compare with current tree to check if it's necessary to update
             # it.
-            changes = tree - current_tree
-            if tree and len(changes) == 0:
+            if tree == current_tree:
                 logger.debug(
                     f"Current and new trees for file {editor.fname} are the "
                     f"same, so no update is necessary"