And Francis, were he to go to confession - whether he is a pope or not, the majority of the Catholic world recognizes him as such; by virtue of his baptism he is a member of the Church- would have to publicly retract his many sins.  Because his sins are in the public domain, he would be required to issue a public retraction of them.  It would be no different than Madonna were she to go to confession.  Her public sins would require a public retraction.

It's clear to me that Pius XII placed the sins of heresy, schism and apostasy in a class all their own.  They are not like other sins. Until I see Church docuмents/support on how these specific sins should be handled or treated, it remains "complicated".

Yes, the part about public retraction, or public abjuration of heresy is what Stubborn is missing.

PUBLIC heresy, PUBLIC schism, etc (i.e. like Martin Luther's) require PUBLIC displays of apology.  This is what canon law says.
If it's a private matter of heresy/schism (where scandal was minimal) then such can be forgiven through confession alone.

But Stubborn is just lumping everything into 1 category.  As he normally does.  Lack of distinguishing.

It's no different than the sin of theft. 
a.  Yes, you can go to confession.  No, you are not forgiven until you make restitution to the person you stole from.

Sin of public heresy/schism:
a.  Yes, you can go to confession.  No, you are not forgiven until you publicly make restitution for your scandal, because your neighbor was hurt due to your sins.

Well, all I can say is start looking. I suggest, seriously, start with searching for sins that are not forgiven in the sacrament of penance, this should shorten your search time considerably.

I attached a pdf snip from Trent on the Sacrament of penance and Extreme Unction, it's less than 11 pages, hopefully you are able to study it.  Here are a few pertinent quotes:

What of all the anathemas then?  Trent lists all the situations where, if one were to believe XYZ, "let them be anathema".  In other words, they are condemned and separated from the Church.  Trent does not speak of what happens to those unfortunates, and it is those situations which I believe Pius XII speaks of when he classifies the sins of heresy, schism and apostasy as separate from all other sins. So, basically, I don't think your pdf covers what I have been speaking about here.  Maybe you have another Church docuмent/teaching that does?

On the idea that the penitent must publicly retract his sins...
"For the rest, as to the manner of confessing secretly to a priest alone, although Christ has not forbidden that
a person may,--in punishment of his sins, and for his own humiliation, as well for an example to others as for the edification of the Church that has been scandalized,-- confess his sins publicly, nevertheless this is not commanded by a divine precept; neither would it very prudent to enjoin by any human law, that sins, especially such as
are secret, should be made known by a public confession."

Personally, I used to think that in the case of public heretics such as the conciliar popes and hierarchy, a public abjuration of their heresies should be an absolute requirement, but per Trent above, it's not, and what I think doesn't matter - and per Trent I was wrong to think that way.

On the Reservation of Cases
Which means sins to which the censure of excommunication is attached reserved to the Holy See. (i.e. only the pope can forgive) is not in force when the penitent is in danger of death....

No, it's right in one sense but wrong in another sense.  It depends.

No, it’s wrong in all senses. A heretic is not a Catholic.