I am no expert on Catholic Tradition,
but it would be helpful for a Pope,
speaking Ex Cathedra,
hence Infallibly in issues of Faith and Morality
To formally put this point to rest.
It is a Major Stumbling Block in
relations between Catholics and Protestants
The point is already put to rest, infallibly. It’s infallible dogma that “outside the Church, there is no salvation”. But since the earliest times, no one (save for some fringe people who didn’t speak for the Magisterium) took that to mean that “one needs to be a visible, explicit, participating member of a Catholic parish, or else one will go to hell”!
Look up the Catholic teachings about “baptism of desire” and “baptism of blood”, to start; these are age-old teachings (not necessarily with those official titles, depending on the source) which show that the Church has never declared that “all non-Catholics are going to hell”.
Put in its clearest sense, the teaching says, “Anyone who is saved, is saved in and through Christ’s Catholic Church... whether they’re aware of that fact, or not... and whether they agree with that fact, or not.”
The “Ex Cathedra” issue is a particular sticking point. My understanding is that this seldom happens, maybe once in a lifetime (I have had several Catholics point this out to me.)
It points to the Sacred/Secular dichotomy heresy that is part and parcel of Roman Catholicism. That a pope may be as evil as Satan, but may, in another altered state, declare infallible Church doctrine, is the epitome of error.