Uncomment the code that hides the material tab in the toolbox. Just for

master.<<

plugins/Toolbox/resources/qml/ToolboxHeader.qml

@@ -34,7 +34,6 @@ Item
             }
         }
 
-        /* Hide for 3.4
         ToolboxTabButton
         {
             text: catalog.i18nc("@title:tab", "Materials")
@@ -47,7 +46,6 @@ Item
                 toolbox.viewPage = "overview"
             }
         }
-        */
     }
     ToolboxTabButton
     {

plugins/Toolbox/resources/qml/ToolboxInstalledPage.qml

@@ -65,7 +65,6 @@ ScrollView
                 }
             }
         }
-        /* Hidden in 3.4
         Label
         {
             visible: toolbox.materialsInstalledModel.items.length > 0
@@ -103,6 +102,5 @@ ScrollView
                 }
             }
         }
-        */
     }
 }