I'm wrestling with the problem of keeping small group common knowledge around and up to date in the face of expiration and regular deletion of chats in free channels (e.g. Slack). This is similar to the problem that early Usenet had, when you couldn't count on any specific message being available because various sites had expiration times in the weeks to small number of months range for postings.
Having a shared wiki - or at least a thing that has wiki nature - sounds like it should be an answer. It needs to have a "recent changes" feed to stay relevant so that people who care can see what's new. Otherwise if new changes are invisible the whole thing goes stale very fast.
Slack "canvases" are appealing, but I fear putting too much into a free system that could change their usage policies. They have a lot of nice functions even on a free plan, with a one-channel-per-canvas structure. Relying on something free to keep long-term knowledge seems like a risk.
Monthly FAQ posts? That was what Usenet did. I'm not sure if monthly is the right pace, but periodic copying out of things that need to be said more than once has proven effective in the distant past. It's not clear that people used to search or even AI will reread the repetitive texts.
