There are certainly many things one can learn from the Western Schism and compare some such actions of Catholics during that crisis to the crisis of our own time.

Question(s):

1) Should the material error of St. Vincent Ferrer when naming Benedict XIII in the Canon of the Mass as Pope be equated with naming Leo XIV in the Canon now?

2) How were the papal claimants during the Western Schism essentially DIFFERENT than the post Vatican II claimants?

Claim(s):

I do not think any of 3 papal claimants during the Western Schism were public, manifest, heretics.
(I am open to being corrected on that if credible evidence of heresy can be produced).

I believe that the docuмents of Vatican II contain heresies.
(Which, in essence, is what differentiates the Western Schism from the current crisis - concerning the above questions.)

I believe that If Benedict had been a manifest public heretic, Vincent would not have named him in the Canon of the Mass.

Therefore St. Vincent naming antipope Benedict XIII in the Canon of Mass was only a material error and not a sacrilegious act because he and many others were only in material error about who the actual Pope was.

Hence, when evaluating which action one should take regarding holding communion with heretical popes the actions of St. Vincent et. nal. should not be equated in this matter.

Annex:
If you do not believe the post-Vatican II claimants are manifest public heretics, then none of the above is relevant to you.

I will go with St. Robert's assessment of Pope Honorius over that of +Lefebvre's.
In fact, it was mainly Protestants that accused him of heresy, while Catholic authors generally defended him from this charge.

Also, notice how it is citing CathInfo as a source! Maybe Matthew doesn't need to make a "Catholic AI" after all!

AI sources aside, St. Robert's position and many others on Honorius is well docuмented.

There is no comparison to the hypothesis of what to do in the case of manifest, public heretical Pope between Honorius and the post-Vatican II claimants.

You certainly may choose to keep quoting +Lefebrve as if he was you infallible rule of faith who holds the answer to every issue with this crisis.

But you have not addressed the main claims of the OP in any substantial way.

To be fair, I suppose it could be taken that you do NOT hold that either the docuмents of Vatican II contain heresy and/or the post-Vatican II putative popes have committed manifest public heresy.

In such a case as I stated above in the Annex, the whole OP would be irrelevant to you, because the issue for you is not that official heresy is coming from the "popes" manifestly and publicly, rather they are just "in error" and "hurting the Church", "leading bad", etc. In such a case if true, then that would demolish my entire argument.

So if that is what you are arguing then there is nothing more to be said between us on this topic.

But, if you do agree that the docuмents of Vatican II contain heresy and the post-Vatican II claimants are manifest public heretics then you have "skin in the game".