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.
Oh, I forgot about this site. I certainly can use it to do proof-of-concept for ideas here, but I’m thinking more of beyond me. A wider-used tool (and imo with more/better categories)
Users can create feeds too: https://piefed.social/feeds