Still, there are lots of great and active groupchats on TG, Discord, Slack, RocketChat, nostr, and Matrix. They're just more fragmented and focused.

Have a look at all the tech you use for LN (nodes, web GUIs, tooling, etc.) Most of those tools will advertise chat servers where the devs hang out and answer questions. Join them and be active and you may get invited to some more private groups where the real alpha gets leaked.