How can one identify the Antichrist, can he be a Bishop opposing the Papacy in relation to 1 John 2:19-20?

Impossible to say as we do not know who he is as of yet. The Early Church Fathers believe that he would be of Hebrew descent: a Jew. For them it was the only possible way to deceive the Chosen People: a false Messiah.

These type of questions are speculative in nature and the Church never pronounces officially in such matters. Anything is possible.

Prophecy is usually recognized as true while the thing prophesized have run their course. This would apply to the Antichrist also the anti-church and anti-gospel of Pope John Paul II should be seen as something the against the Church and against the Gospels and not as a counterfeit church or a counterfeit gospel, although the Antichrist will no doubt teach a false gospel of sorts.

That said I am sure that one will be able to find a possible interpretation that the Antichrist could be either a bishop or an anti-pope. Do not mean that it is true.

A prophecy of St. Francis of Assisi seems to indicate the that either the Antichrist or one of his satellites could be an anti-pope elected uncanonically. Thus he would be at Last a bishop, if not a cardinal.

Prophecy of St. Francis of Assisi (d. 1226): “There will be an uncanonically elected Pope who will cause a great schism, there will be diverse thoughts preached which will cause many, even those in the different orders to doubt, yea, even agree with those heretics which will cause my Order to divide, then will there be such universal dissensions and persecutions that if those days were not shortened even the elect would be lost.” (Rev. Culleton, The Reign of Antichrist, Tan Books, 1974, p. 130.). Some believe this prophecy referred to the controversy surrounding the election of Pope John XXIII and Cardinal Siri. But it could refer to the next and last pope (Peter the Roman). The last pope may just cut Catholics loose from unity and the papacy, causing total disruption and confusion. - Malachy's Prophecies - The Last 10 Popes

In fact, Blessed Anne Catherine Emmerich speaks of such a possibility in her revelations that the Antichrist could be a false pope.

“Last night, from eleven to three, I had a most wonderful vision of two churches and two Popes and a variety of things, ancient and modern. I shall relate, as well as I can, all that I remember of it. My angel guardian came and told me that I must go to Rome and take two things to the Pope, but I cannot now recall what they were— perhaps it is the Will of God that I should forget them. I asked my angel how I could make so long a journey, sick as I was. But when I was told that I should make it without difficulty, I no longer objected. An odd-looking vehicle appeared before me, flat and slight, with only two wheels, the flooring red with white edges. I saw no horses. I was gently lifted and laid on it and, at the same instant, a snow-white, luminous child flew toward me and seated himself at my feet. He reminded me of the Patience child in green, so sweet, so lovely, and perfectly transparent. He was to be my companion, he was to console and take care of me. The wagon was so light and smooth that at first I was afraid of slipping off; but it began to move very gently of itself without horses, and I saw a shining human figure going on ahead.

The journey did not seem long, although we crossed countries, mountains, and great waters. I knew Rome the instant we reached it, and I was soon in the presence of the Pope. I know not now whether he was sleeping or praying, but I had to say two things to him, or give him two things, and I shall have to go to him once again to announce a third. Then I had a wonderful vision. Rome suddenly appeared as in the early ages, and I saw a Pope (Boniface IV) and an emperor whose name I knew not (Phocas). I could not find my way in the city, all was so different, even the sacred ceremonies; but yet I recognized them as Catholic. I saw a great round building like a cupola— it was a pagan temple full of beautiful idols. It had no windows, but in the dome was an opening with a contrivance for keeping out the rain. It seemed as if all the idols that ever existed were gathered together there in every conceivable posture. Many of them were very beautiful, and others exceedingly odd; there were even some of geese which received divine honor. In the center of the building stood a very high pyramid formed entirely of those images. I saw no idolatrous worship at the time of which I speak, although the idols were still carefully preserved. I saw messengers from Pope Boniface going to the emperor and petitioning for the temple to be changed into a Christian church. I heard the latter declaring distinctly that the Pope should allow the ancient statues to remain, though he might erect therein the Cross to which the highest honors should be paid. This proposal, as it seemed to me, was made not wickedly, but in good faith.

I saw the messengers return with the answer and Boniface reflecting as to how he might in some measure conform to the emperor’s will. While he was thus deliberating, I saw a good, pious priest in prayer before the crucifix. He wore a long white robe with a train, and an angel hovered by his side. Suddenly he arose, went straight to Boniface, and told him that he should by no means accede to the emperor’s proposal. Messengers were then dispatched to the emperor, who now consented to the temple’s being entirely cleared. Then I saw his people come and take numbers of the statues to the imperial city; but still many remained in Rome. Then I saw the consecration of the temple, at which ceremony the holy martyrs assisted with Mary at their head. The altar was not in the center of the building, but against the wall. I saw more than thirty wagon-loads of sacred relics brought into the church. Many of them were enclosed in the walls and others could be seen through round openings covered with something like glass.

When I had witnessed this vision even in the smallest details, I saw again the present Pope and the dark church of his time in Rome. It seemed to be a large, old house like a town hall with columns in front. I saw no altar in it, but only benches, and in the middle of it something like a pulpit. They had preaching and singing, but nothing else, and only very few attended it. And lo, a most singular sight! Each member of the congregation drew an idol from his breast, set it up before him, and prayed to it. It was as if each man drew forth his secret thoughts or passions under the appearance of a dark cloud which, once outside, took some definite form. They were precisely such figures as I had seen around the neck of the illicit bride in the Nuptial House, figures of men and animals. The god of one was short and broad with a crisp head and numerous, outstretched arms ready to seize and devour all in its reach; that of another was quite small with miserable, shrunken limbs; another had merely a block of wood upon which he gazed with rolling eyes; this one had a horrible animal; that one, a long pole. The most singular part of it was that the idols filled the place; the church, although the worshippers were so few, was crowded with idols. When the service was over, everyone’s god re-entered into his breast. The whole church was draped in black, and all that took place in it was shrouded in gloom.

Then I saw the connection between the two Popes and the two temples. I am sorry that I have forgotten the numbers, but I was shown how weak the one had been in adherents and human support, but how strong in courage to overturn so many gods (I knew the number) and to unite so many different forms of worship into one; and, on the contrary, how strong in numbers and yet how irresolute in action was the other since, in authorizing the erection of false temples, he had allowed the only true God, the only true religion to be lost among so many false gods and false religions.

It was also shown me that those pagans humbly adored gods other than themselves, and that they would have been willing to admit in all simplicity the only God, the Most Holy Trinity. Their worship was preferable to that of those who adore themselves in a thousand idols to the total exclusion of Our Lord. The picture was favorable to the early ages, for in them idolatry was on the decrease, while in our days it is just the contrary. I saw the fatal consequences of this counterfeit church; I saw it increase; I saw heretics of all kinds flocking to the city. 2 I saw the ever-increasing tepidity of the clergy, the circle of darkness ever widening.

And now the vision became more extended. I saw in all places Catholics oppressed, annoyed, restricted, and deprived of liberty, churches were closed, and great misery prevailed everywhere with war and bloodshed. I saw rude, ignorant people offering violent resistance, but this state of things lasted not long. Again I saw in vision St. Peter’s undermined according to a plan devised by the secret sect while, at the same time, it was damaged by storms; but it was delivered at the moment of greatest distress. Again I saw the Blessed Virgin extending her mantle over it.

In this last scene, I saw no longer the reigning Pope, but one of his successors, a mild, but very resolute man who knew how to attach his priests to himself and who drove far from him the bad. I saw all things renewed and a church which reached from earth to Heaven. I saw one of the twelve new apostles in the person of the young priest whom the unchaste bride wanted to marry. It was a very comprehensive vision and portrayed anew all that had been previously shown me regarding the Church’s destiny. On another occasion, I had a vision of the Vicar-General’s stanch resistance to secular power in behalf of the interests of the Church. The affair covered him with glory, 3 though upon some other points he was to blame. I was told that I should have to go again to the Pope; but when all this will take place I cannot say.”

Schmoger, Very Rev. K. E.. Life and Revelations of Anne Catherine Emmerich Volume 2 (with Supplemental Reading: A Brief Life of Christ) [Illustrated] (Kindle Locations 3740-3797). TAN Books. Kindle Edition. - Anne Catherine Emmerich and the Two Popes

Even Archbishop Fulton J. Sheen (1948) spoke about the possibility of a counterfeit Church:

“[Satan] will set up a counterfeit church which will be the ape of the [Catholic] Church… It will have all the notes and characteristics of the Church, but in reverse and emptied of its divine content.”

“We are living in the days of the Apocalypse, the last days of our era. The two great forces – the Mystical Body of Christ and the Mystical Body of the anti-Christ – are beginning to draw battle lines for the catastrophic contest.”

“The False prophet will have a religion without a cross. A religion without a world to come. A religion to destroy religions. There will be a counterfeit Church.”

“Christ’s Church the Catholic Church will be one; and the false Prophet will create the other.” - Things Accelerate Toward the End – Prophecy of Archbishop Fulton Sheen

True or false time will tell!

Spiritual revolt using Church's authority

Cardinal Manning, the most prominent father at the First Vatican Council who was responsible for the definition on papal infallibility, said in his Temporal Power of the Vicar of Christ 2nd part (4 lectures), "The Perpetual Conflict of the Vicar of Christ", pp. 81-173 (available in printed form from TradiBooks as The Pope and The Antichrist) that the spiritual "revolt" of 2 Thessalonians 2:3-11 will occur from the authority of the Church, so it seems likely that Antichrist, the leader of that revolt, will also come from the Catholic Church:

We have here [2 Thessalonians 2:3-11] a prophecy … of a [spiritual*] revolt, which shall precede the second coming of our Lord … The authority, then, from which the revolt is to take place is that of the kingdom of God on earth, prophesied by Daniel [cf. Daniel 2] as the kingdom which the God of heaven should set up … in other words, the one and universal Church, founded by our Divine Lord, and spread by His Apostles throughout the world. In this one only kingdom was deposited the true and supernatural pure theism, or knowledge of God, and the true and only faith of God incarnate, with the doctrines and laws of grace. This, then, is the authority from which the revolt is to be made, be that revolt what it may.

^{[*"St. Jerome, with some others, interprets this revolt to be the rebellion of the nations or provinces against the Roman Empire. … They have revolted, and no manifestation has appeared." Thus, the revolt is spiritual, not temporal.]}

Beginning 2 ¶¶ later, Cdl. Manning describes the characteristics of the revolt (pp. 85-6):

1. "schism, as given by St. John"

   1 John 2:18-19
   Little children, it is the last hour; and as you have heard that Antichrist cometh, even now there are become many Antichrists: whereby we know that it is the last hour. They went out from us, but they were not of us. For if they had been of us, they would no doubt have remained with us; but that they may be manifest, that they are not all of us.

2. "rejection of the office and presence of the Holy Ghost."

   Jude 1:19
   These are they, who separate themselves, sensual men, having not the Spirit.

3. "the denial of the Incarnation."

   2 John 1:7
   For many seducers are gone out into the world, who confess not that Jesus Christ is come in the flesh: this is a seducer and an antichrist.

"These, then, are the marks by which, as the Church is to be known by her notes, the antichristian revolt, or apostasy, may be distinguished."

Antichrist likely an anti-pope

It's likely that Antichrist is an anti-pope, either a true pope that subsequently apostatizes or an invalidly elected false pope pretending to be the true pope.

The commentary on 2 Thessalonians 2:4 (that Antichrist "sitteth in the temple of God") of the very anti-Protestant Original Reims New Testament says:

St. Augustine therefore li. 20 de civit. c. 19 and St. Jerome q. 11 ad Algasiam. do think, that this sitting of Antichrist in the temple, doth signify his sitting in the Church of Christ, rather than in Solomon's temple. Not as though he should be a chief member of the Church of Christ, or a special part of his body mystical, and be Antichrist and yet withal continuing within the Church of Christ, as the Heretics feign, to make the Pope Antichrist (whereby they plainly confess and agnise [recognize] that the Pope is a member of the Church, & in ipso sinu Ecclesia, and in the very bosom of the Church, say they:) for that is ridiculous, that all Heretics whom St. John calleth Antichrists as his precursors, should go out of the Church, and the great Antichrist himself should be of the Church, and in the Church, and continue in the same. And yet to them that make the whole Church in revolt from God, this is no absurdity. But the truth is, that this Antichristian revolt here spoken of, is from the Catholic Church: and Antichrist, if he ever were of or in the Church, shall be an Apostate and a renegade out of the Church, and he shall usurp upon it by tyranny, and by challenging worship, religion, and government thereof, so that himself shall be adored in all the Churches of the world which he list to leave standing for his honor. And this is to sit in the temple or *against the Temple of God, as some interpret. If any Pope did ever this, or shall do, then let the Adversaries call him Antichrist.

This passage makes it clear that a true pope cannot be Antichrist, but Antichrist will be an anti-pope, and anti-popes are not members of the Church.

^{taken from: "What is the Catholic interpretation of 2 Thessalonians 2:3?" (that Antichrist "sitteth in the temple of God")}