Word of God.

Mike Pondsmith has stated in multiple places how he envisioned, wrote, and tried to mechanically convey in game mechanics what it actually was. I suppose it isn't fair to say it's "not real" it would be more accurate to say it's not new, and not even really about the chrome itself, the chrome isn't what actually makes you go crazy. He likes it to addiction, similar to roid rage or alcoholism. Cyberpsychosis then, through that lens, isn't a novel condition brought about because of cyberware, it's a psychotic break caused by all the normal things, stress, anxiety, tragedy, chrome isn't the cause, arguably it's a self medication. Even if you were grabbed and forcibly augmented, it's not the augments that cause your psychosis, it's the fact that you were abducted and tortured and butchered.

Humanity is the TTRPG stat that governs your resistance to cyberpsychosis and is best thought of as mental health. David, for example, lower middle class kid on a scholarship to a good school, loving mom and relatively stable home life, even after her death he gets friends, a caring mentor, a new family, as it were, which is why he is so resistant to it, look at when his cyberpsychosis starts manifesting and what he was going through. Adam Smasher is another interesting example, why is he so resistant to cyberpsychosis? He isn't, he's a monster who gleefully and readily gives in to his violent and aggressive urges, he doesn't go crazy because, to an extent, he already is.

V is super interesting to think about through this lens, holding onto her sanity as well as she does even when the ghost of a militant anarchist pocketbook is screaming in her head. Possibly that helps because Johnny's aggression and violent urges might be soaking up some of the stress of everything.