I'm in a few but I'm not particularly active on many recently. The RPGdesign subreddit has one, and its the only dedicated game design server I'm I'm as of now, but then you have to interact with Reddit users. I also talk into a relative void on Twitter sometimes. 

Should we start one?

I run a Queer Game Dev server with a ttrpg dev channel. You don't have to be queer to join as long as you're respectful and follow the rules. https://discord.gg/AxVTMrH

I'm still thinking about it. Mostly because discord (not so much specific communities) has been making my increasingly uncomfortable lately. (For context, I'm a huge introvert, so notifications are an issue on phone.)