Muting doesn’t prevent everyone else from seeing it, only yourself.

Zapvertisements refer to the top zap on a note appearing as the first comment under the note, which is a new feature in Damus testflight. So someone can zap a note with an image or anything attached and have it appear under someone’s note as the first comment kind of like an ad. Anytime someone opens a note to read the comments, the first thing they’ll see is the Zapvertisements