Created attachment 7268 
A screenshot of the issue

Some packages only provide icons in sizes much bigger than the standard
GTK menu size of 16px.

The clipboard manager qlipper for example provides the following icon:
/usr/share/icons/hicolor/128x128/apps/qlipper.png

In GTK 3.22.18 the function gtk_image_new_from_icon_name when given
GTK_ICON_SIZE_MENU as second argument still returns an image with 128x128.

The patch I have supplied uses existing code to scale such an image. 

diff --git a/garcon-gtk/garcon-gtk-menu.c b/garcon-gtk/garcon-gtk-menu.c
index 41990f2..f31a1ed 100644
--- a/garcon-gtk/garcon-gtk-menu.c
+++ b/garcon-gtk/garcon-gtk-menu.c
@@ -650,7 +650,11 @@ garcon_gtk_menu_load_icon (const gchar *icon_name)
   gtk_icon_size_lookup (GTK_ICON_SIZE_MENU, &w, &h);
   size = MIN (w, h);
 
-  if (! gtk_icon_theme_has_icon (icon_theme, icon_name))
+  if (gtk_icon_theme_has_icon (icon_theme, icon_name))
+    {
+	  pixbuf = gtk_icon_theme_load_icon (icon_theme, icon_name, size, 0, NULL);;
+    }
+  else
     {
       if (g_path_is_absolute (icon_name))
         {
@@ -684,22 +688,23 @@ garcon_gtk_menu_load_icon (const gchar *icon_name)
               g_free (name);
             }
         }
+    }
 
-      /* Turn the pixbuf into a gtk_image */
-      if (G_LIKELY (pixbuf))
-        {
-          /* scale the pixbuf down if it needs it */
-          GdkPixbuf *tmp = gdk_pixbuf_scale_simple (pixbuf, w, h, GDK_INTERP_BILINEAR);
-          g_object_unref (pixbuf);
-          pixbuf = tmp;
+  /* Turn the pixbuf into a gtk_image */
+  if (G_LIKELY (pixbuf))
+    {
+      /* scale the pixbuf down if it needs it */
+      GdkPixbuf *pixbuf_scaled = gdk_pixbuf_scale_simple (pixbuf, w, h, GDK_INTERP_BILINEAR);
+      g_object_unref (G_OBJECT (pixbuf));
 
-          image = gtk_image_new_from_pixbuf (pixbuf);
-          g_object_unref (G_OBJECT (pixbuf));
-        }
+      image = gtk_image_new_from_pixbuf (pixbuf_scaled);
+      g_object_unref (G_OBJECT (pixbuf_scaled));
+    }
+  else
+    {
+	  /* display the placeholder at least */
+	  image = gtk_image_new_from_icon_name (icon_name, GTK_ICON_SIZE_MENU);
     }
-
-  if (image == NULL)
-    image = gtk_image_new_from_icon_name (icon_name, GTK_ICON_SIZE_MENU);
 
   return image;
 }