We do not have the legal authority to depose a false Pope, you are right. But we do not need to have him legally deposed in order to know that he is a heretic and an anti-Pope.
Wrong. You're not an anti-pope until you’re deposed or legally declared a formal heretic. St Bellarmine already told us what to do in the face of a pope who ACTS LIKE a heretic - resist and ignore him. There is no world where a pope can be called a heretic by the laity. Our opinion is meaningless.