I found the commentary on "moral outrage porn" here very useful, especially since it grants that moral outrage IS in fact appropriate and indeed necessary in some circumstances. That's not something I see in most discussions of the subject.
It's still only a couple of a paragraphs in an opinion piece, however, so it is a fuzzy concept and I can see it being weaponized upon falling into the wrong hands. Perhaps it already has, since this piece was published in 2019.
Because really, it's not necessarily easy to tell whether someone else is consuming moral outrage porn or whether they are expressing outrage as part of a genuine moral engagement with the issue in question.
So ultimately I think it's better used as something to apply introspectively, to reflect on how-- and, when, and indeed whether-- you are engaging morally with issues that spur you to outrage.