Question: The point of this is to create 100 topics from a list. When this is done my application will go through this list once every day to check for upcoming events. A message will be sent to the subscribed users if the app finds an event on a particular topic. I will also try to implement some logic to check if there are users subscribed to this particular topic.

Answer: 
Two parts to your question:

Firebase topic subscription is officially documented only for devices. In other words, only devices with device tokens can subscribe to a topic. Look at AWS SNS topics for topics on which other applications can subscribe.

Secondly, for your use case, topics may not be the solution. Generally, a topic is not like a queue from which you can retrieve a message. Generally, a topic will only send messages to subscribers already actively subscribed to the topic. If there is no subscriber on the topic when a message is received, the message disappears.
AFAIK, I don't think this is possible. The way I understand how Topics work is that (from my answer [here](https://stackoverflow.com/a/37650817/4625829), also mentioned it in my answer [here](https://stackoverflow.com/a/39382345/4625829)):

> 
> a topic is created when there is at least 1 subscriber and it also gets automatically deleted when there are no more subscribers.
> 
> 
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Regardless if it's for web-app or mobile app, having a registration token is necessary for Topic Messaging.