Okay, so where are they? Show us some.

Let's be honest here, how many of these "specialized ultra-nerdy communities" are closed off Discord servers?

To find these spaces, you have to think in reverse. You can’t look for the community first. You have to start by having a specialized interest. You can’t rely on an algorithm to tell you what you care about and how you want to spend the time in your life. That answer has to come from within. Once you have that answer, finding the community online is quite easy.

The way you find them is to search for the creators and other community leaders. For example, let’s say you are interested in a specific video game. Look for the publishers, developers, top players, live streamers, and media coverage of that game. Those people are likely to be hosting or participating in communities that you can join, even if they are closed Discord servers.