My understanding is that in the simulator you can simulate notifications by drag-dropping a suitable JSON file onto the simulator - or with some command-line that achieves the same thing. I don't know what you've read, but maybe it was referring to that functionality?
This is something that has changed over time and googling finds lots of old suggestions of how to do it that are probably redundant...
Topic:
UI Frameworks
SubTopic:
SwiftUI
Tags: