Thanks for your kind words.
Regarding fanout. Yes exactly. Fanout doesn't mean it needs to involve SQS just it can involve SQS. It is also called a fanout pattern if you do a A2P and only notify Emails, SMS, etc.
To your second question how the architecture would look like for different preferences of architecture.
I think the main benefit of that architecture is that customer can subscribe to a topic. That means if your user A subscribes to the topic for Email and not in-app notification that is fine. It would be also just the one topic.
The consumer/subscriber has the power to subscribe and unsubscribe to topics (similar like you can to newsletters basically). That is one of the main benefits.
With a queue the producer would need to define which consumer will get the message and most probably it will be another application.
Does that help? :)