I’m exploring this issue. There is a post about these configs not being maintained since a few years from a few years ago, and judging by the git history that did not change much. My current understanding is that this functionality is not on, and for some reasons might by tricky to enable on yunohost.
My old yunohost server had no real filtering whatsoever, I’ve just cut spam in mailboxes dramatically by following these instructions for setting up rspamd and manually setting training data. So this is a solution for now.
Earlier attempts though gui had no effect, so something in this broader process was missing. Still got another ~6 yunohost servers, so I want to figure out how this should be set up and if possible push changes to the yuno rspamd repo so this is default behaviour. By the looks of it none of the mentioned instructions are in the config files in the ynh repo.