Blocking notifications doesn’t remove this person from view. It just means I don’t get emails about the contributions. If I check out the site, I still see multiple threads of interest torn asunder by the (to me) irritating contributions of this person which may actually be within the rules, but … I don’t care. Things within “the rules” and the “code of conduct” that annoy me still annoy me. Without some capacity to mitigate their appearance, the only other real alternative is to ignore the forum.
And a quick exploration of the meta site for Discourse shows me that this is politically-opinionated software and that user-side blocking like I want is seen as a “misfeature”, so … I guess I have my answer.