Have you checked if "windows notifications" setting inside Settings applet can manage whether it shows or not? It certainly should be there.
Also, you could try "global settings" inside the window you have opened, on the left pane. It should allow for GPU choices.
Ironically, I have one nvidia optimus laptop and I am missing this notification, and suffer from constant issues where application runs on intel instead of nvidia gpu, causing really bad user experience because of poor performance.