Hi,
The answer to your question ultimately depends on your specific use case and the goals you are trying to achieve with your topic organization. However, as a general rule of thumb, it is often better to have a smaller number of broad topics with multiple sub-topics than to have a large number of narrow topics.
Having a smaller number of broad topics with multiple sub-topics can make it easier for users to navigate your content and find what they are looking for. It also makes it easier to ensure that related information is grouped together, which can help users to make connections and gain a deeper understanding of your content.
On the other hand, having a large number of narrow topics can make it more difficult for users to find what they are looking for, particularly if they are not familiar with the specific terminology you are using. It can also make it harder to ensure that related information is grouped together, which can make it harder for users to make connections and understand the context of the information they are reading.
In the case of COVID, a single broad topic with multiple sub-topics may be more appropriate, as there are many different aspects of COVID that users may be interested in learning about, and having a single broad topic can help to ensure that all of these sub-topics are easily accessible and well-organized.