As an aside, Ryan Grant also makes an interesting argument regarding DR's contention that cuм ex can't be abrogated, because parts of it allegedly pertain to divine law:
"But that assumes the prescriptions of cuм ex are of Divine Law, whereas in reality they are not. This bull was abrogated by the 1917 Code of Canon Law which incorporated these penalties,
but never for a pope prior to his election (let alone after). It only says:
Ob tacitam renuntiationem ab ipso jure admissam quaelibet officia vacant ipso facto et sine ulla declaratione, si clericus A fide Catholica publice defecerit. (Can. 188.4)
And:
Omnes a christiana fide apostatae et omnes et singuli haeretici aut schismatici incurrunt ipso facto excommunicationem. (Can. 2314 1.1)
Again, none of these address what to do about the Roman Pontiff. If cuм Ex Apostolatus was still in force, the Code of Canon Law would have taken note of it. The editors of the 1917 Code did not put it in because of the problematic nature of actually enforcing cuм Ex. No dogmatic theology textbook references it, and not one work of ecclesiology from any of the authors you site (Dorsch, etc.) or other recent authors such as Billot, Franzelin, Van Noort, Palmieri or Berry. As the Sedevacantist journal
Sodalitum frankly admits:
'This task [proving an election invalid by the precepts of cuм Ex] however in the current state of affairs, shows itself doubly arduous. To begin with, it is necessary to prove the formal and notorious heresy of the errant one. Failing a (hypothetical) admission of the guilty party, an intervention of the Church and its Magisterium then takes place, in accordance with the words of St. Paul to Titus: “A man that is a heretic, after the first and second admonition, avoid.” What Paul IV perhaps did not foresee—like all the classical writers on the question of the “heretical pope”—was that no authority would arise in such a case to make the admonitions required by scripture and canons.
The second difficulty consists in the current juridical value of the Constitution of Paul VI. The sixth canon of the Code of Canon Law prescribes that what is not taken up again in the 1917 Code should be considered as abrogated, unless the law is evidently by divine right. Now the prescriptions of Paul IV are only partially resumed by the Code (Can. 188.4 and 2314.1) without any mention of the case of the supreme pontiff. Doubt therefore remains about the character of Paul IV’s proclamation—whether it belongs to divine law, and thus is always valid, or to ecclesiastical law.' (
Sodalitium, no. 14 pp. 9-10)
Why would the major Sedevacantist journal in Europe not consider it obvious that the bull of Paul IV still applies if it was so evident that it is of divine right and still in force? For the simple reason that it does not."
https://unamsanctamcatholicam.com/2022/10/23/cuм-ex-apostolatus-and-loss-of-office/