It should be noted that the (visibility of) community bans are a result of better enforcement of site bans in 0.19.4, which for now is implemented by sending out community bans for local communities when a user gets instance banned: github.com/LemmyNet/lemmy/pull/4464
Prior to this, when a user got instance banned from .ml, they were also implicitly banned from .ml communities, but this was only known to the instance they were banned on. As a result, users were still able to post, comment, and vote on those communities, but it would be visible only on that user’s instance, not federated anywhere else. Visibility of this ban was exclusively on the banning instance’s modlog.