He talks about

They went out from us, but they did not really belong to us. For if they had belonged to us, they would have remained with us

So who could be from Christians, but not belong to Christians? Those who willingly serve and support Jews - the children of Satan, who hate Christ. Including their dumb narrative that Jews have any right for any land in Palestine. They completely lost any rights for their "promised land" 2000 years ago when denied and killed Jesus Christ.

So, any "christian" who support Israel is exactly one of that "antichrists" John talk about in 2:18.

Antichrist (with capital letter), will manifest itself in the Third Temple in Jerusalem. It is possible only if state of Israel exist. Only thing that prevent building of Third Temple is Al-Aqsa mosque buit on the place. Only state of Israel could destroy mosque and build Third Temple. So, any "christian" supporting existense of the state of Israel, also support building of the Third Temple and so Antichrist coming. Eventually those "christians" who support illegal state of Israel are exactly those "antichrists" spewed from christians who want and help Antichrist coming. There could not be anything more "antichrist" than wanting Antichrist.

He talks about

They went out from us, but they did not really belong to us. For if they had belonged to us, they would have remained with us

So who could be from Christians, but not belong to Christians? Those who willingly serve and support Jews - the children of Satan, who hate Christ. Including their dumb narrative that Jews have any right for any land in Palestine. They completely lost any rights for their "promised land" 2000 years ago when denied and killed Jesus Christ.

So, any "christian" who support Israel is exactly one of that "antichrists" John talk about in 2:18.