Oh wow, look at that!
Yes, this is why I was looking for an official answer on this. We do not have anywhere else to go for this.
Do comments section is the first place I went to. As you mentioned, it says that UIInteraction is used to register actions triggered by system capture events and should be attached to views in the responder chain. And the for handler, it says that it is called when either the primary or secondary events are triggered.
This is all that exsists on this. No more documentation or sample code. I will be experimenting and will update whatever I find.
This API is significant for developers of 3rd party camera apps, we had to go around many limitations to mimic this action.