I don't think I've ever been in a Discord that was just...generically fannish. Discords in my experience are either:

• based on an existing friend group and grow slightly from there
• are started for a specific reason like a fandom or a fan event, and then they grow additional channels for discussing stuff other than the reason they were launched

So I've got several servers where I generically discuss fandom stuff, but they started because of Les Mis, or MDZS, or in one case fandom federation.