diff --git a/autotests/test_window_paint_data.cpp b/autotests/test_window_paint_data.cpp
--- a/autotests/test_window_paint_data.cpp
+++ b/autotests/test_window_paint_data.cpp
@@ -248,6 +248,9 @@
     bool isX11Client() const override {
         return false;
     }
+    bool isOutline() const override {
+        return false;
+    }
 
 private:
     qreal m_opacity = 1.0;
diff --git a/deleted.h b/deleted.h
--- a/deleted.h
+++ b/deleted.h
@@ -177,6 +177,13 @@
 
     QVector<uint> x11DesktopIds() const;
 
+    /**
+     * Whether this Deleted represents the outline.
+     **/
+    bool isOutline() const override {
+        return m_wasOutline;
+    }
+
 protected:
     virtual void debug(QDebug& stream) const;
 
@@ -229,6 +236,7 @@
     ToplevelList m_transientFor;
     DeletedList m_transients;
     bool m_wasPopupWindow;
+    bool m_wasOutline;
 };
 
 inline void Deleted::refWindow()
diff --git a/deleted.cpp b/deleted.cpp
--- a/deleted.cpp
+++ b/deleted.cpp
@@ -53,6 +53,7 @@
     , m_wasWaylandClient(false)
     , m_wasGroupTransient(false)
     , m_wasPopupWindow(false)
+    , m_wasOutline(false)
 {
 }
 
@@ -149,6 +150,7 @@
     m_wasWaylandClient = qobject_cast<ShellClient *>(c) != nullptr;
     m_wasX11Client = !m_wasWaylandClient;
     m_wasPopupWindow = c->isPopupWindow();
+    m_wasOutline = c->isOutline();
 }
 
 void Deleted::unrefWindow()
diff --git a/effects.h b/effects.h
--- a/effects.h
+++ b/effects.h
@@ -442,6 +442,7 @@
     bool keepBelow() const override;
     bool isModal() const override;
     bool isPopupWindow() const override;
+    bool isOutline() const override;
 
     KWayland::Server::SurfaceInterface *surface() const override;
     bool isFullScreen() const override;
diff --git a/effects.cpp b/effects.cpp
--- a/effects.cpp
+++ b/effects.cpp
@@ -1832,6 +1832,7 @@
 TOPLEVEL_HELPER(bool, skipsCloseAnimation, skipsCloseAnimation)
 TOPLEVEL_HELPER(KWayland::Server::SurfaceInterface *, surface, surface)
 TOPLEVEL_HELPER(bool, isPopupWindow, isPopupWindow)
+TOPLEVEL_HELPER(bool, isOutline, isOutline)
 
 #undef TOPLEVEL_HELPER
 
diff --git a/effects/fade/package/contents/code/main.js b/effects/fade/package/contents/code/main.js
--- a/effects/fade/package/contents/code/main.js
+++ b/effects/fade/package/contents/code/main.js
@@ -43,6 +43,9 @@
     if (!w.visible) {
         return false;
     }
+    if (w.outline) {
+        return false;
+    }
     if (w.deleted && effect.isGrabbed(w, Effect.WindowClosedGrabRole)) {
         return false;
     } else if (!w.deleted && effect.isGrabbed(w, Effect.WindowAddedGrabRole)) {
diff --git a/effects/fadingpopups/package/contents/code/main.js b/effects/fadingpopups/package/contents/code/main.js
--- a/effects/fadingpopups/package/contents/code/main.js
+++ b/effects/fadingpopups/package/contents/code/main.js
@@ -42,6 +42,11 @@
         return true;
     }
 
+    // Maybe the outline deserves its own effect.
+    if (window.outline) {
+        return true;
+    }
+
     // Override-redirect windows are usually used for user interface
     // concepts that are expected to be animated by this effect, e.g.
     // popups that contain window thumbnails on X11, etc.
diff --git a/effects/glide/glide.cpp b/effects/glide/glide.cpp
--- a/effects/glide/glide.cpp
+++ b/effects/glide/glide.cpp
@@ -319,6 +319,11 @@
         return false;
     }
 
+    // Dont't animate the outline because it looks very sick.
+    if (w->isOutline()) {
+        return false;
+    }
+
     // Override-redirect windows are usually used for user interface
     // concepts that are not expected to be animated by this effect.
     if (w->isX11Client() && !w->isManaged()) {
diff --git a/effects/scale/package/contents/code/main.js b/effects/scale/package/contents/code/main.js
--- a/effects/scale/package/contents/code/main.js
+++ b/effects/scale/package/contents/code/main.js
@@ -66,6 +66,11 @@
             return false;
         }
 
+        // Dont't animate the outline because it looks very sick.
+        if (window.outline) {
+            return false;
+        }
+
         // Override-redirect windows are usually used for user interface
         // concepts that are not expected to be animated by this effect.
         if (window.x11Client && !window.managed) {
diff --git a/internal_client.h b/internal_client.h
--- a/internal_client.h
+++ b/internal_client.h
@@ -55,6 +55,7 @@
     bool isInternal() const override;
     bool isLockScreen() const override;
     bool isInputMethod() const override;
+    bool isOutline() const override;
     quint32 windowId() const override;
     using AbstractClient::resizeWithChecks;
     void resizeWithChecks(int w, int h, ForceGeometry_t force = NormalGeometrySet) override;
diff --git a/internal_client.cpp b/internal_client.cpp
--- a/internal_client.cpp
+++ b/internal_client.cpp
@@ -211,6 +211,14 @@
     return false;
 }
 
+bool InternalClient::isOutline() const
+{
+    if (m_internalWindow) {
+        return m_internalWindow->property("__kwin_outline").toBool();
+    }
+    return false;
+}
+
 quint32 InternalClient::windowId() const
 {
     return m_windowId;
diff --git a/libkwineffects/kwineffects.h b/libkwineffects/kwineffects.h
--- a/libkwineffects/kwineffects.h
+++ b/libkwineffects/kwineffects.h
@@ -2066,6 +2066,15 @@
      **/
     Q_PROPERTY(QWindow *internalWindow READ internalWindow CONSTANT)
 
+    /**
+     * Whether this EffectWindow represents the outline.
+     *
+     * When compositing is turned on, the outline is an actual window.
+     *
+     * @since 5.16
+     **/
+    Q_PROPERTY(bool outline READ isOutline CONSTANT)
+
 public:
     /**  Flags explaining why painting should be disabled  */
     enum {
@@ -2354,6 +2363,11 @@
      **/
     virtual QWindow *internalWindow() const = 0;
 
+    /**
+     * @since 5.16
+     **/
+    virtual bool isOutline() const = 0;
+
     /**
      * Can be used to by effects to store arbitrary data in the EffectWindow.
      *
diff --git a/outline.cpp b/outline.cpp
--- a/outline.cpp
+++ b/outline.cpp
@@ -180,6 +180,9 @@
         } else {
             m_mainItem.reset(m_qmlComponent->create(m_qmlContext.data()));
         }
+        if (auto w = qobject_cast<QQuickWindow *>(m_mainItem.data())) {
+            w->setProperty("__kwin_outline", true);
+        }
     }
 }
 
diff --git a/toplevel.h b/toplevel.h
--- a/toplevel.h
+++ b/toplevel.h
@@ -216,6 +216,13 @@
      **/
     Q_PROPERTY(bool popupWindow READ isPopupWindow)
 
+    /**
+     * Whether this Toplevel represents the outline.
+     *
+     * @note It's always @c false if compositing is turned off.
+     **/
+    Q_PROPERTY(bool outline READ isOutline)
+
 public:
     explicit Toplevel();
     virtual xcb_window_t frameId() const;
@@ -283,6 +290,7 @@
 
     virtual bool isLockScreen() const;
     virtual bool isInputMethod() const;
+    virtual bool isOutline() const;
 
     /**
      * Returns the virtual desktop within the workspace() the client window
@@ -764,6 +772,11 @@
     return false;
 }
 
+inline bool Toplevel::isOutline() const
+{
+    return false;
+}
+
 inline QRegion Toplevel::damage() const
 {
     return damage_region;
diff --git a/unmanaged.h b/unmanaged.h
--- a/unmanaged.h
+++ b/unmanaged.h
@@ -47,6 +47,7 @@
         return UnmanagedLayer;
     }
     NET::WindowType windowType(bool direct = false, int supported_types = 0) const;
+    bool isOutline() const override;
 
 public Q_SLOTS:
     void release(ReleaseReason releaseReason = ReleaseReason::Release);
@@ -57,6 +58,8 @@
     virtual ~Unmanaged(); // use release()
     // handlers for X11 events
     void configureNotifyEvent(xcb_configure_notify_event_t *e);
+    QWindow *findInternalWindow() const;
+    bool m_outline = false;
 };
 
 } // namespace
diff --git a/unmanaged.cpp b/unmanaged.cpp
--- a/unmanaged.cpp
+++ b/unmanaged.cpp
@@ -28,6 +28,7 @@
 
 #include <QTimer>
 #include <QDebug>
+#include <QWindow>
 
 #include <xcb/shape.h>
 
@@ -81,6 +82,9 @@
     getWmOpaqueRegion();
     getSkipCloseAnimation();
     setupCompositing();
+    if (QWindow *internalWindow = findInternalWindow()) {
+        m_outline = internalWindow->property("__kwin_outline").toBool();
+    }
     if (effects)
         static_cast<EffectsHandlerImpl*>(effects)->checkInputWindowStacking();
     return true;
@@ -159,11 +163,27 @@
     return info->windowType(NET::WindowTypes(supportedTypes));
 }
 
+bool Unmanaged::isOutline() const
+{
+    return m_outline;
+}
+
 void Unmanaged::addDamage(const QRegion &damage)
 {
     repaints_region += damage;
     Toplevel::addDamage(damage);
 }
 
+QWindow *Unmanaged::findInternalWindow() const
+{
+    const QWindowList windows = kwinApp()->topLevelWindows();
+    for (QWindow *w : windows) {
+        if (w->winId() == window()) {
+            return w;
+        }
+    }
+    return nullptr;
+}
+
 } // namespace