However, Unam Sanctum doesn’t allow that escape provision Roman Catholics love to fly to when the pope says something they don’t like.
Unam Sanctum is itself not recognized as an infallible document by the Church. It was much criticized in its own day through today for the over reach by the pope. Indeed if would be ridiculous to take your interpretation of it seriously as that would force what I believe as part of the faith to flap in the breeze of who ever is the current pope, or with Francis, daily with what ever idea passes through his head most recently.
The heart of the Catholic Faith is an unwavering, constant teaching that is consistent from the time of the apostles through the early church Fathers upto today. That is what I hold to against all the damnable heresies from early agnostics to Arius to Luther and up to the present day’s neo-Gnosticism.