See, I'm the opposite. I've got a Discord server, which are very much "where my friends are": If I make an acquaintance (or any of my friends do), they get added to the server. Some stick around, and get woven into the social fiber. Some never come back, and eventually get removed from the server during our annual purge. There's maybe 10-20 active people (i.e., people we see at least a couple times a month), a handful of regulars that are that multiple times a week, and then maybe twice all that again of people we hear from once in a blue moon. If I want to chat, I'll hop in voice. If I want to share something I found, I'll stick it in a text channel.

There's still plenty of communities on the internet. It's just that the communities worth belonging to are not wide open to the public. Community building does not scale.

I agree, I feel similarly. There are now 25+ car groups on fbook that I have to subscribe to, because the main web-board / usenet group for that car doesn't get anywhere near as much traffic as it used to. Major vendors are providing support on fbook - which sucks.