I'm still happy with our self-hosted mattermost.
No AI stuff, so far as what I've seen. I think you can connect to AI services, but it doesn't seem like it's forced into it.
I've used Zulip, and it's okay. At least when I used it, it wasn't quite slick enough. It was weird enough (e.g., clunky image posting) that people didn't use it much.