I was looking through preferences and realized there’s no option to BLOCK someone from sending you a message, rather you can only allow certain people to message you, which is a Whitelist.
There’s a feature that allows you to ignore certain users. Even though it isn’t exactly a block, you’ll not receive any notifications from them + you’ll be unable to see any message/topic they’ve sent. That’s currently the only workaround. In order to use this feature, go to the profile of the person you wish to ignore. Then, click the notification status button (it should be either muted or normal) and choose “Ignored”.
This only takes effect when a new post is created by that user or when you view an older one from that user (fun fact: if you have still ignored me then this post will be replaced with this: “Ignored content”). Other than that, it actually acts like a mute.