As per subject
That’s on me, and also the reason why it hasn’t been done (work obligations have been trumping everything else for the past two years for me, KTLO stuff).
Slack doesn’t have an “archive functionality” unless you pay for it, which is quite expensive. You can still access old messages, but in a form that’s not quite useful, which is why it requires extracting the information and transforming it programmatically. We have a few options for this but they all require some work upfront which I’ve had to procrastinate on (see above).
What format are the old messages in? Can I have access to them?
Yes, you can: Export your workspace data | Slack
One way to read them is using in your PC the “Slack export viewer” (GitHub - hfaran/slack-export-viewer: A Slack Export archive viewer that allows you to easily view and share your Slack team's export)
Can a slack admin send me the exported workspace data?