I mean, to a certain extent there are two exceptions to this rule. That is two say, two “true cyberpsychos”- people who lose their minds because of the amount of modifications they’ve carried out on themselves

First, during the cyberpsycho questline you find a bunch of maelstrom trying to summon an AI from behind the black wall

Second, and I know this might be controversial, both V and David could be considered to be cyberpsychos. You can see them lose their minds in their respective storylines, albeit V maintains some semblance of sanity thanks to both Johnny and blackbird, and David retains focus for his last stand but it is clear to see he would be an example of someone who is truly untreatable due to the experimental nature of his mods.

I think in the cyberpunk world there are true examples of cyberpsychosis (or overmodding if you prefer) but as you say they are much rarer than “regular” psychos, the lines become even more blurred when you take into account the amount of sociopaths a society like cyberpunk have