These are the largest servers I'm in. Each of these servers has (one or more) general chat channels as well as channels for finding/posting job opportunities, game dev resources, networking, or streamer outreach, as well as a decent amount of activity, but the size, vibe and focus of each of these servers is slightly different from the last.
Indie Dev and Creators: https://discord.gg/gGDAyt9tNW - This server was created by several game developers on Twitter who are uncertain about the future of that platform. The server is not that strict on who is allowed in - there are roles for streamers, content creators, reviewers and fans of indie games as well, but most people and most activity is from developers.
D3v Central Station: https://discord.gg/d3vcentralstation - This server is more industry-oriented, there's more variety in which roles you can select and a huge list of channels sorted by topic, but none for people who don't work in or with indie games in some capacity.
How To Market A Game (HTMAG): https://discord.gg/ePJ2u3XhTM - Conversations here are more focused on, well, getting eyeballs on your game, or how other people managed to get eyeballs on theirs.
There's also a decent amount of communities on Reddit aimed at game developers or game development, of which https://www.reddit.com/r/gamedev/ is the biggest one, and with a decent variety of contributors at various skill levels (from AAA to indie to student). Though if you want to start a discussion that is more technical in nature (like a topic about developing a game in a certain engine or language), you will likely be told to post it in a subreddit for that particular engine/language instead.