I’ve gotten myself in a bit of a corner with a non-Christian friend who basically is attempting to make the case since all the Gospels have a list of those being at the crucifixion of Christ, but only the Gospel of John lists John himself as being one of them, that it is suspect that he actually was. Now, I 100% believe John was there and 100% believe that the all the Gospels are divinely inspired, but how do I explain John’s omission from the other lists?
Even in his own Gospel, John doesn’t quite name himself. He habitually calls himself “the disciple whom Jesus loved” (cf. John 19:26). The explanation for why the synoptic Gospels exclude him, and for why John refers to himself only indirectly, may be as simple as that John, in his humility, might not have wanted recognition for staying with Jesus during his crucifixion while the other apostles fled.
Beyond speculation though, we don’t know the reason why John wasn’t mentioned in the other Gospels as having been present at the crucifixion. But the fact that he was not does not discredit his own account that he was there. You could offer this as an analogy: Suppose someone wrote a memoir in which he mentioned that he had witnessed the Twin Towers collapse on 9/11. If he was not mentioned in other accounts of that event as a witness, would that automatically prove that his own account was not credible?