There are tricks to get messages from Slack, though I heard they were changing soon if not already. A year or so ago I exported all messages from a Slack group

There are tricks to get messages from Slack, though I heard they were changing soon if not already. A year or so ago I exported all messages from a Slack group I ran and used a Discord bot to recreate the entire dataset including channels and user posts. So we now have our entire history of messages without being blocked by a paywall (Until Discord does the same, and we'll be off to find a new home).