I have been trying to set up auto-moderation or, at least, be able to ban a "Guest" IP address that keeps spamming my site despite having hCaptcha on, etc. Sadly, we need a guest-friendly forum so people can ask questions before joining our site.

Is there a way to ban a guest's IP address?

Thanks and Warmest Regards!

You can utilize the Ban Settings in ACP -> Members -> Ban Settings. However, it would be strongly encouraged to not allow guest posting as you will always deal with spam in this configuration.