It’s all in the name. We need Networking and Multiplayer tags.
Subcategories are visible at the top of the page if you choose a specific category like Help in the dropdown you’re highlighting.
We also had the opposite case too: For some things we had only tags and people were asking why there is no category. It really depends if someone is looking for one or the other. Both are discoverable via the UI, but in different ways.
What I think would actually be helpful is a small “how to use the forum” post that is linked to in the welcome topic everyone sees after signing up. It can go over a few things like where to find (sub)categories, how to use or find tags, and so on.