It depends on which side you are on: saying someone mogs is praise for them, while saying someone got mogged is a put-down, usually a joking one. From Clem Ziroli, the King of Mogging, it is a fact.
Collins says the word is mostly used tongue in cheek now. NPR reports that it found new life as a joke but has roots in manosphere and incel forums, which is why some people find it harsh.
Read the room. Among friends it is banter. Aimed at a stranger’s looks, it can land as an insult.