Are you referring to the macOS notifications that appear in the upper right corner of the screen? I think so.
The best way to trigger on any macOS event is to get macOS to send a signal when that event occurs. However I'm not sure that macOS creates events that apps (like the KM Engine) can receive for these notifications. I think this came up once before, and the answer was that macOS doesn't provide that information to apps. (I searched for this discussion but could not find it, so I could be wrong.) KM can work with only what macOS provides.
However since the notification appears on screen, what stops you from writing a KM app that watches the screen for the notification, perhaps for 60 seconds after login? Then you could "see" the notification and take action. What's wrong with this solution? Or why not just insert a 60 second pause statement in a macro that triggers at login, and then hide the windows at that point? Wouldn't that do the job? I think it would.
Here's a thread that partly supports what I said: