When installing GC in Unity 2019.2.1f1, only two error appeared and the GC toolbar didn't.
Changed GameCreatorToolbar.cs as below.
line 103: SceneView.duringSceneGui += OnPaintToolbar;
line 115: SceneView.duringSceneGui -= OnPaintToolbar;
Saved and toolbar then appeared.
onSceneGUIDelegate is obsolete. Suggest next version of GC includes this update for future compatibility.
Customer support service by UserEcho