So is it probable that individual members of the faithful are authorized to make the judgment whether the Pontiff is heretic? Are we all left to our consciences in this regard?
There is no else to make the call either, e.g. the CDF head, Muller, is a heretic himself and denies the Bodily Resurrection of Our Lord.
We STILL have not had a pope become a heretic because the post-1958 crop were all formal heretics before being elected, thus their elections were null and void. Ratzinger's works were on the Index as suspect of heresy in the 1950's
Check out section 7 of Cum Ex Apostolatus Officio at the link in comment 40. In it Pope Paul IV says the laity can withdraw with impunity from any heretic pretending to hold authority and can call on the scular government to evict any heretic who refuses to leave.
Section 6 that I posted says even if unanimous election by all cardinals and despite any passage of time the election would still be void.
Even if they were not heretics before their elections and had become heretics after becoming genuine popes, then they still would be out on their rear ends for heresy as the Church teaches - but God saved us fro that as they were inelegible beforehand.
The salvation of souls is the highest law, and anyone who follows and acts on the teaching of these heretical non-popes is jeopardizing his own.
Christ and the Church did provide for this in advance as the teaching is clearly laid out.