Get all classes with interface

I am trying to setup an event system using interfaces in blueprint. Basicly, I want to implement observer interfaces everywhere, and in the player controller, to send messages to all observers through interfaces.

Generally it works well with getAllActors with interface. However, suppose the HUD is an observer, or widget is, or whatever class that isn’t an actor is an observer, how then, do I use an interface to send a message to them?

NOTE: I do NOT want to get a reference to the HUD, widgets or whatever. All my blueprints communication is through event system with interfaces. I obviously know I can just use getHUD, but I want to do it through interfaces, this is perfectly doable in any language, java c++ whatever.

I want to do the exact same thing. Did you ever find an answer?

For a HUD, I got this answer from Discord:

Make a BP that holds the only reference to the widget.
Implement the interface in the BP.