For people who actually care about the truth (unlike those with false piety).
The Vatican II Popes could be considered to be mere material heretics until they sinned against the commandment "Thou shalt not have another god before me". Because this is part of natural law, we can presume that anyone who sins against this commandment is not a material heretic but a formal one.
And I am being generous by pretending the Vatican II Popes before then were merely material heretics.
I never thought of it like that. Could you back this up with a quote about the intention of someone who violates the first commandment?
How do you know they intend to violate the commandment? What if they intend to do what they deem is in conformity with Catholic teaching?