I made the !gamedev@sh.itjust.works community here and I'm not sure how to advertise it. I don't want to be obnoxious about it but I have to admit discoverability here is kinda bad
Just post stuff. If someone finds it interesting, they'll comment on it, and before you know it, you'll have built a community. I just started one myself, not really stressing myself out over it :)
if you have any questions about finding or subscribing to these federated communities, !LemmyTips@discuss.tchncs.de has some good posts like this one: https://sh.itjust.works/post/124476