I think you’ll get varied answers on the last one–of course I think mine is right, lol

! IMO, there’s been a tendency to minimize papal infallibility in recent decades (some even say there is only two instances!–compare that to the relatio which says “thousands and thousands”–a bit hyperbolic, but you get the point!).
According to
the CDF commentary on the Profesio Fidei, as well as the relatio I linked to earlier, the Pope may definitively judge ex cathedra not just dogma (divinely revealed doctrines to be
believed with divine and Catholic faith). It also covers doctrines which are *sententia definitive tenenda *(doctrines, which while not formally revealed, are connected to revelation by logical necessity and which are necessary for defending and expounding upon it. These must be definitively
held.). In addition, dogmatic facts are also covered (dogmatic facts are historical facts connected to revelation by necessity–they include canonizations of saints, the validity or invalidity of non-Catholic sacraments, etc.).
So, given all that, it would be the last canonization. However, excluding dogmatic facts, unless I am missing a more recent one, that would probably be in 1995, when Bl. John Paul II in Evangelium Vitae made three such definitive judgments, confirming murder, abortion, and euthanasia as contrary to the moral law. For example:
“Therefore, by the authority which Christ conferred upon Peter and his Successors, in communion with the Bishops-who on various occasions have condemned abortion and who in the aforementioned consultation, albeit dispersed throughout the world, have shown unanimous agreement concerning this doctrine-I declare that direct abortion, that is, abortion willed as an end or as a means, always constitutes a grave moral disorder, since it is the deliberate killing of an innocent human being.”
vatican.va/holy_father/john_paul_ii/encyclicals/documents/hf_jp-ii_enc_25031995_evangelium-vitae_en.html
***Regarding Ordinatio Sacerdotalis, which was in 1994, the wording of the definitive judgment follows Vatican II’s definition of papal infallibility essentially word for word. Note, that doctrine was defined as *sententia definitive tenenda (*to be definitively held), so it is not considered a revealed dogma. That may be where some confusion lies. But as I mentioned above, such doctrines may also be proclaimed infallibly by the Pope.