https://wdtprs.com/2021/06/the-question-of-two-popes-bothers-a-lot-of-people-some-thoughts/
What an odd post. The good priest, who is not a canonist, cites the canonical claims of Bullets Barnhardt even though she has never studied or practiced Canon Law.
Here is the professional conclusion of this problem by a famous Canon Lawyer, a man Fr. Z. has cited many times in the past.
What the 1983 Code does say, as did the 1917 Code, is this: “Only those laws must be considered invalidating … which expressly state that an act is null …” (c. 10, olim c. 11). Because no canon of the 1983 Code, under which Benedict XVI submitted his resignation (c. 332 § 2), addresses the quality of the Latin used in papal documents, let alone does any canon make the Latinity of papal documents go to their validity, I say, odd question answered: bad Latin does not mean that one must remain pope.
https://canonlawblog.wordpress.com/2014/10/01/lighter-fare-can-bad-latin-save-a-papacy/
Two small but persistent arguments attack the very foundation of Francis’ papacy: first, Benedict XVI’s resignation was invalid (take your pick as to reasons why, but mostly because of pressure allegedly brought on Benedict, as supposedly evidenced by his resignation wording), so there was no vacant Holy See to fill, and so a conclave could not elect a pope; or, second, various irregularities were committed before or during the conclave itself, so the election of Francis was invalid.
Both sets of arguments are offered in inexcusable ignorance of Canon 10 (which sets a high standard indeed for declaring any kind of ecclesiastical acts invalid, etc.), but the arguments alleging the invalidity of Benedict’s resignation are so vacuous that no time will be spent refuting them here. On the other hand, some (okay, basically one) of the claims that irregularities allegedly committed in the conclave itself resulted in an invalid election do have a modicum of plausibility and deserve at least a brief hearing.
https://canonlawblog.wordpress.com/2017/09/28/francis-was-never-pope-call-me-unpersuaded/
Why didn't Fr. Z. turn to his Canon Lawyer friend for the answer to this problem rather than to sow discord and confusion?