Most of them would accept Nancy Peℓσѕι as pope.
And you would have to say that you're not 100% certain that she's not pope.
Uhm, no.
If Francis died today and a conclave elected Nancy Peℓσѕι in a few weeks time you would have to say - she's not the pope but I can't be 100% certain.
If you disagree please explain why. And please explain why you would be 100% certain that Peℓσѕι wouldn't be pope but you are not 100% certain about Bergoglio.
Because Nancy Peℓσѕι isn't even legitimate "matter" to be the Pope. She couldn't even be materially pope, much less formally. What requires the intervention of Church authority is when there are allegations that an actual MATERIAL pope has formally lost the office. Peℓσѕι can't even be material pope. It's really not that hard, Heremenegild.
The qualifications to be a validly elected Pope can be found in the Church Canonical Law. What happens in the case of a heretical pope cannot. Canon 332-1 of the 1983 Code states that one already a bishop (not necessarily a cardinal) who
accepts legitimate papal election becomes pope immediately. One who is not yet a bishop (and the Church has elected several non-bishops to the papacy) can accept election, but must be immediately consecrated bishop.
That means that the Roman Pontiff must:
1. Be a male and be willing
2. Be Baptized,
3. Be an ordained deacon, priest, and bishop, and
4. Have the use of reason in order to accept election and, if necessary, holy orders
There is simply not consensus as for what to do in the case of the election of an actual heretical Pope. Also, heresy (material or formal) is the pertinent denial of a Catholic dogma. The only doctrine that the conciliar Popes can be guilty of denying is the EENS dogma, as written, which ironically most traditionalist do anyway.
It is de fide that the Pope can be judged by none in this world, he may be rebuked and corrected, but that would need to happen by the Church like John XXII who submitted himself to a commission on his heretical teaching of the Beatific Vision.