Nobody disputes the pope is the rule of faith, but it is a different issue than whether or not his election has received UPA (which is antecedent to whether or not he is acting as the rule of faith).
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It's not really a different issue if being the rule of faith is an inherent part of being pope, and Cardinal Billot says that it is. To separate the two would be like saying, "I accept that that shape is a triangle, but I don't accept that it has three sides." Since a lot of people didn't accept Paul VI as their rule of faith in 1962, they didn't peacefully accept him as the pope. And certainly he wasn't accepted peacefully in the way that John XXIII was accepted peacefully by the whole Church, who had no clue what lay in store for them in 1958.

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I'm not saying that's a clear slam-dunk argument. I'm not 100% behind it myself. I'm more offering it as a possible answer to the question of whether Paul VI received UPA. It's certainly an interesting fact that John XXIII apparently received UPA and did not come out openly as a heretic the way Paul VI did, who did not receive the same acceptance that John XXIII had. It looks like there may have been some supernatural force restraining John XXIII from going too far, which did not restrain Paul VI. But these are probably things we won't know until the last day.
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Regarding the latter, he acts as the rule of faith when his teachings are magisterial (ie., universality one both time and space); when he teaches at the level of the authentic magisterium (which is not actually magisterial at all, for lack of temporal universality, or contradiction of same), he is not acting as a rule of faith, but as a private doctor (even when he cloaks his errors under the guise of council, encyclical, more proprietary, etc).
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This is yet another discussion

but my short answer is that a real pope is always acting as the rule of faith when he teaches the whole Church, no matter through what medium or in what format, and does not (and cannot) lead the Church astray in those circuмstances. Cf. Cardinal Billot: "For it would be the same thing for the Church to adhere to a false pope, as it would be to adhere to a false rule of faith, since the pope is the living rule which the Church must follow in believing and always in fact follows."