Assuming that macOS has APIs that support this, there should be KM triggers for the following:
Screen Saver starts
Screen Saver ends
Notification Center starts
Notification Center ends
Launchpad starts
Launchpad ends
Mission Control starts
Mission Control ends
Application Windows starts
Application Windows ends
Desktop starts
Desktop ends
If you aren't sure what some of those items mean they are listed in the System Settings for Hot Corners.
I was looking into this because I wanted "Hot Corners" to trigger a KM macro, but there doesn't seem to be a way to do that. Perhaps someone here can investigate whether it's possible to trigger an app using the Hot Corners Shortcuts feature of macOS.
If there is no way to trigger a KM macro using Hot Corners, then maybe there could be a new KM trigger in a future update that triggers a KM macro based on which corner the mouse is moved to (or, alternatively, which edge of the screen the mouse is moved to. That would suffice.) This week I've written a macro which polls the value MOUSEX() and executes a macro if MOUSEX()=0, and it's a delightful way to "trigger" a macro. But it would be so much better if I didn't have to poll.
Yay. I think many people will like this, once they've tried it. I've been simulating this for a week with a polling macro, and I enjoy it a lot.
Just be aware that there are two features in macOS both called "Hot Corners." One is the feature I listed above, the other is a feature in the Accessibility / Keyboard Preferences pane that is very hard to find. It looks like this: (notice, it has the exact same name)
Oddly enough, these two features, both called Hot Corners, are not mutually exclusive. You can use both methods at the same time, and TWO things will happen when you move the mouse to a corner of the screen.
Very interestingly, if you turn on the Accessibility's Hot Corners feature, you can use KM to click the mouse on the screen (i.e., a right click, left click, or double click) simply by using some method (like a KM action) to move the mouse to a position on the screen. No "click" action is required. I've tried it, and it works. The only downside to this method is that macOS seems to have some code that goes out of its way to avoid clicking the mouse if it thinks the mouse was moved "accidentally." I'm not sure why someone would need to do this feature (or the macOS error-correction feature) other than its intended purpose, which is to help people who are mobility-challenged. But I'm keeping it in my toolkit.
Just one more tip. I'm not sure how Hot Corners work on a multi-monitor configuration when the Display is Extended. It probably prioritizes one of the two "upper left" corners as the real one. I'm not sure if it's the one that's "most upper" or "most left".
On my setup, which is two displays side-by-side, it's logically what you'd expect: Upper and lower left corners of the left display, and upper and lower right corners of the right display.
If I had them set up on some sort of diagonal, I have no idea what it would do :).
The accessibility one also has a cute little display that shows you it is thinking about triggering a hot corner behaviour and you should get out of there if you don't want that to happen.
Such triggers sound tempting. In fact, they can be, especially if you can set a delay time so that they are not triggered unintentionally. And if the "opposite" is also possible, meaning that something is triggered when the mouse leaves the corner.
But to be honest, I stopped using them again. In order not to trigger unintentionally, I had to set the delay so high that it seemed too long when I actually wanted to trigger something. I'm not sure if anyone understands this
