When someone is in an objectively evident state of mortal sin, the Church has not just a right but a duty to warn them away from full participation. This has been upheld from the earliest days and the interpretation of “judge not” you are working from is a modernist innovation.
God judges the ultimate destination of the soul but those who will not listen to the admonishments of the Church will be lost.
This pope is the head of this church. And he says, worry about your self and stop judging others.
He is the visible head of the Church but he cannot unilaterally change the teachings of the Church. Even popes have been corrected for heresy and papal infallibility covers only a very narrow set of conditions. Look at the history of what the Church teaches to find the truth. Your interpretation of judging is not consistent with the long history of Church teaching.
He is not. Jesus Christ is the head of the Catholic Church. And Jesus Christ condemned adultery.