I am using the interstellar app and enabled that the instance is always shown.

If I see something I don't like I hit either instance, magazine or the user, after the respective site opens up I hit the block sign.

edit: to unblock I open the explore tap and filter for blocked

Blocking users or magazines works, as previously mentioned.

Alternatively, you could just use the subscription view and only subscribe to the magazines you want.

One other option, is that you could create a Filter List that blocks specific words you find frequently in the posts you don't like, such as "anime".