It's virtually impossible to do so in Slack, unless someone ponies up the cash, which is not viable for very large slacks.

I agree with the fact that Slack/Discord are terrible for keeping track of things long-term, but I will say that once you've set Discord/Slack up and running, operating it is typically pretty smooth - you've already likely got Slack and Discord running, and you can check it every so often.

Granted, things can completely explode, and moderation is still a requirement, but that's true of forums as well.

(Although due to their async nature, things boil over much more slowly, and it's typically easier to just put the entire forum or a user into a timeout.)

Why not use a facebook page? Super easy to maintain and some moderation