"Suapte natura" is the term that Pope Pius XII uses in the Latin.

“Public heretics (and a fortiori, apostates) are not members of the Church.  They are not members because they separate themselves from the unity of Catholic faith and from the external profession of the faith.  Obviously, therefore, they lack one of the three factors-baptism, profession of the same faith, union with the hierarchy-pointed out by Pius XII as requisite for membership in the Church (see above, p. 238).  The same pontiff has explicitly pointed out that, unlike other sins, heresy, schism, and apostasy, automatically sever a man from the Church. ‘For not every sin, however grave and enormous it be, is such as to sever a man automatically from the Body of the Church, as does schism or heresy or apostasy‘ (MCC 30, italics ours).”
(Monsignor G. Van Noort, S.T.D., Dogmatic Theology, Volume II, Christ’s Church, 153)

Read that the sin of heresy "automatically" severs a man from the Church.  Why?  Because the sin of heresy "suapte natura" (by its very nature) does so.

Meg, you are resisting the meaning of "suapte natura".  In your wrong interpretation, "suapte natura" does not apply to the pope in regards to the effect of the sin of public heresy.  You are resisting what is in the very definition of "suapte natura", that is, it applies in ALL cases.  Abortion is "suapte natura" evil (i.e., in ALL cases).  Likewise, the public sin of manifest formal heresy "suapte natura" separates the heretic from the Church (i.e., in ALL cases).

Yes.  It does.  Heresy "suapte natura" separates the heretic from the Church, as taught by Pope Pius XII.

"The Canon Law commentary of the Pontifical Faculty of Canon Law of the University of Salamanca explains that the sole necessary condition for such a loss of office to take place, is that the act be freely committed, and then the loss of office follows necessarily: 'El hecho por el que se presupone la renuncia debe ser puesto voluntariamente, a tenor del canon 185; pero, cuмplida esta condición, la perdida del oficio se produce necesariamente.' That the canon is applicable to all ecclesiastical offices is stated explicitly with the words, 'quælibet officia vacant ipso facto' – and therefore necessarily includes the office of the Supreme Pontiff. The Very Rev. H. A. Ayrinhac explained, in his General Legislation in the New Code of Canon Law, on Loss of Ecclesiastical Offices, that such loss of office (Canons 185-191) 'applies to all offices, the lowest and the highest, not excepting the Supreme Pontificate.' (p. 346)"

Kramer, Paul. To deceive the elect: The catholic doctrine on the question of a heretical Pope . Kindle Edition.

By the term "suapte natura".

Again, just someone's opinion. Not actual Church teaching.