In the first two images, you know that your projectile is actually hitting something, and therefore the Event Hit is triggered.
In this case, where you want to change a static mesh of some actor, the widget doesn’t know what actor to change the static mesh on, unless you tell it. You can create a new variable on the widget, and make it of type DestructiveWall (you actually don’t need to cast then, as the variable knows what type it is), then on the button click, you’d change the static mesh of your referenced actor. Here’s a simple blueprint to show what I mean:
I’ve marked the interesting things with orange. You’re welcome to ask any questions regarding this solution, and I’ll do my best to answer them 