Back with newsgroups the general rule was to go from general to specific. You start with a general discussion group and when discussions about video games get annoying you create a games group. If then there are too many Baldur’s Gate discussions you create BG. If they are dominated by Baldur’s Gate 3 you create a Baldur’s Gate 3 group. If everyone is fawning over Withers you create a Withers group which of course will be flooded with discussion about the Withers’ tits mod, which shall get its own group.
Meaning you should create a group when demand is there and not the other way around.
The generalist advice only works for topics that are not controversial. If there is any outrage in the discussion talking in the general area will be very negative and never get into the core issue you want to discuss
As someone who runs multiple niche health and diet communities I can literally feel the burn everytime the topic comes up in a general discussion.
Here is a community promo post for a diet community https://hackertalks.com/post/8398344 50% downvotes and 31 comments all negative
Here is the first introduction post for the community https://hackertalks.com/post/5677435 75% downvotrs, and 40ish all negative comments
I’m just trying to illustrate how anything controversial needs to be protected and sheltered for meaningful growth. All the negativity that can be delivered has a real chilling effect on new user participation