Something I found dismaying was just how only a few of the subreddit communities I liked had any alternative platforms to go to: only the fountain pens community had a Discord server. And upon joining that server the day before the blackout, it was pretty clear just how much work had already gone into making that community feel immediately welcoming (looks like it took at least a year) and ready to handle huge influx of new users.

Given that Christian Sellig made his criticism of the API changes public only 11 days prior to the blackout and made his decision to close down Apollo only 3 days prior, most subreddits just wouldn't have the chance to get started elsewhere, regardless of whether it's Discord or Lemmy or whatever. Discord arguably requires among the least amount of technical savvy to use among the alternatives, but ensuring it doesn't become instant chaos is a nontrivial social problem. And certainly, 11 days to break the inertia of 100k+ users to move elsewhere is nontrivial as well.