PV, Journet is explaining the same process described in Canon Law that I explained. He is doing it in a very roundabout way.
But a single Latin phrase used by Journet, expresses exactly what I was telling you:
Papa haereticus non est depositus sed deponendus.
That is, he is not immediately "deposed," but he will be "deposed" after the second and third steps are taken (See Titus 3:10-11 and Canon 2314).
But this is what you are missing, even though the "Papa hereticus" is not immediately "deposed," according to 2314.1, he still "incurs by the fact [ipso facto] excommunication." Immediately upon his public manifestation of heresy, he is automatically excommunicated. No declaration by any authority is necessary to establish ipso facto excommunication.
Here is an excerpt from John of St Thomas which will help you understand what Cardinal Journet is defending:
Answer:
I answer [to Bellarmine] that the heretic should be avoided after two admonitions legally made and
with the Church’s authority, and not according to private judgment; indeed, a great confusion in the Church would follow , if it was allowed that the admonition is made by
a private man, and that the manifestation of this heresy having been made without being declared by the Church and proclaimed to all, in order that they avoid the Pontiff, that all should be required to avoid; for
a heresy of the Pope cannot be public for all the faithful on the report of a few, and this report, not being legal, does not require that all believe it and avoid the Pontiff; and therefore as the Church proclaims him legally elected by legally designating him for all, it is necessary that she deposes him by declaring and proclaiming him as a heretic to be avoided.
Therefore, we see that this has been practiced by the Church, when in the case of the deposition of the Pope, the cause itself was first addressed by the General Council before the Pope was declared “No Pope”, as we said above. Therefore it is not because the Pope is a heretic, even publicly, that he will
ipso facto cease to be Pope, before the declaration of the Church, and before she proclaims him as “to be avoided” by the faithful.
And when St. Jerome says that a heretic separates itself from the body of Christ, he does not exclude a judgment of the Church, especially in such a serious matter as the deposition of the Pope, but it indicates only the quality of the crime, which excludes
per se from the Church, without any further sentence, at least from the moment he is declared [heretic] by the Church; indeed, even if the crime of heresy separates itself (
ex se) of the Church, however, in relation to us that separation is not understood as have been made (
not intelligitur facto) without this statement.
It is the same thing from the reason added by Bellarmine. A non-Christian who is such in itself AND in relation to us (
quoad se et quoad nos) cannot be Pope; however, if he is not in itself a Christian, because he has lost the faith, but if in relation to us he is not legally declared being infidel or heretic, as obvious as it may appear in a private judgment,
he is still in relation to us (quoad nos) a member of the Church and therefore the head. Accordingly, a judgment of the Church is required through which he is declared (
proponatur) as being a non-Christian and to be avoided, and then
he ceases in relation to us to be the Pope, consequently, previously he did not cease to be himself (
etiam in se) [Pope], because all what he did was valid in itself.
1https://dominicansavrille.us/on-the-deposition-of-the-pope-part-2-of-2/(emphasis belongs to the post on the Dominican website)