Report blatant self-plagiarism to journal editor or PubPeer?
Taking the complaint public shames both the author and the journal, which may be counterproductive if the journal is responsible and willing to act promptly (mistakes do happen, even for very good journals).

I would thus recommend starting by reporting to the journal, which should have a procedure for dealing with such things.  If the journal does not take you seriously or refuses to act, then take it public and shame both the author and the journal.