I think these posts should be removed, for breaking the spam rule. They don’t add anything to the discussion. If you don’t have anything to say, please just like the post instead of posting one word.
Likes are actually limited so sometimes people can’t do that.
I personally don’t mind single word replies as long as they relate to the topic. Like for example, making a post about a game suggestion, someone saying “yes” is all I’d need t know they like the idea, assuming they can’t just like the post.
But I’d imagine doing that repeatedly is definitely spam.
I think the limit keeps posts more meaningful and “forum-like”. I don’t really get the point of single word replies. In my opinion the replies should have at least some content and be meaningful for a longer time. We already have Discord where you can spam one-liners and emojis.
But at the end of the day, it’s all about how the users want the forum to be like. If the limit isn’t good, it can be edited or removed.
Just replying “yes” doesn’t make a lot of sense, either. Why not make a poll if the point of the topic is to ask a yes/no question? Maybe you want to quote someone and clarify it with a “yes”, but doesn’t the quote count towards the 20 character minimum?
I have seen another Discourse forum’s actively applying warnings (and removing offending posts) to people that bypassed the character limit (30 characters on there). They have also banned the words “30 characters”, “30 chars” “30 chaaaaaaaaaaaaaaaaaaars”, etc.
But I do not feel that there is a need to Ban users that bypass it.