Cloning this repo, building, and running as-is works perfectly thanks to the project-lock.json. (I believe this might be why the issue was overlooked.) But running npm install @nodegui/nodegui within a new project and copying over the example source files shows missing or differing API elements.
The example project is using @nodegui/nodegui v0.6.5
The latest version at this time is @nodegui/nodegui v0.12.1
QPushButtonEvents has been renamed to QPushButtonSignals; This object also seems to be treated differently than before, so the snipped QPushButtonSignals.clicked will not work.
BaseWidgetEvents has been removed.
I would advise amending the project.json file so as to limit support to that last compatible version of the package. (running npm update on this example will break it)