Update overview workarea on monitor focus change

#2183

overview.js

@@ -128,7 +128,7 @@ export const Overview = class {
                             else
                                 box[focusedPanel.fixedCoord.c1] += size
                         } else if (isBottom)
-                            // The default overview allocation is very good and takes into account external 
+                            // The default overview allocation takes into account external 
                             // struts, everywhere but the bottom where the dash is usually fixed anyway.
                             // If there is a bottom panel under the dash location, give it some space here
                             box.y2 -= focusedPanel.geom.h

panelManager.js

@@ -328,6 +328,14 @@ export const PanelManager = class {
             Main.overview._overview.add_constraint(new Layout.MonitorConstraint({ index: monitor.index }));
 
             Main.overview._overview._controls._workspacesDisplay._primaryIndex = monitor.index;
+
+            // https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2395
+            // The overview allocation used to calculate its workarea based on the monitor where the overview
+            // was displayed, but it got changed back to always use the primary monitor. So now, temporarily assign 
+            // the primary monitor to dtp focused monitor while recalculating the overview workarea
+            Main.layoutManager.primaryMonitor = monitor
+            Main.overview._overview._controls.layout_manager._updateWorkAreaBox()
+            Main.layoutManager.primaryMonitor = Main.layoutManager.monitors[Main.layoutManager.primaryIndex]
         }
     }