At this moment I have to visit the community to use the UI to block, but some communities are so extremely nsfw that I don't really want to open them to block them. It would be very handy to be able to use the option for 'create report / block user' to also include 'block community'
I know I can also block communities in the settings, but the above mentioned option would be more user friendly imho.
In Jebora, you can try to block a community via a post by pressing 3 dots icon then click "block [community name]". I think you even can block the community without open the post in the home page
In web ui i think there is no way to do that yet
Also check your nsfw settings by unchecking "show nsfw content"
If that's not what you wanted, I suggest you open a feature request in Lemmy's repository or lemmy-ui's repository
Edit: fix formatting
The Voyager app just recently added the ability to block a community directly from the feed without opening the post or the community.