Basic bionic replacements don’t really affect people much in the setting, it’s more the really invasive and extensive modifications that leave someone permanently dependent on a cocktail of medications and which require frequent invasive maintenance work that end up fucking people up when they can’t afford the meds or the maintenance work anymore. So instead of like a prosthetic leg think about something extremely invasive IRL, like having a bunch of pins put in everywhere to fix a ton of broken bones after a traumatic accident and how that can cause lifelong problems with chronic pain (my old neighbor had that after being hit by a car as a teen and some fifty years later he still has issues with them and has to have occasional checkups to make sure they’re not falling apart - at least from what I gathered talking to him), except instead of being a bunch of static parts that just hold someone together inside imagine a system of hydraulics, artificial muscles, reinforcing anchors, and nervous system taps running on electronics that heat up and wear out over time, that can glitch out and cause painful spasms as the artificial muscles fire at odds with one’s organic muscles, etc.

I don’t think that would be directly causing brain damage just by being hooked up, but when it starts to degrade and malfunction, when someone has to go off or ration the meds that stop their body from rejecting the implants, that’s probably going to cause some brain damage just from the constant stress and pain and sleep deprivation it would cause to say nothing of potential random electric shocks delivered directly into the nervous system from a malfunctioning CPU.

Also in Cyberpunk Edgerunners David’s implant is a fucking high-end sandevistan, a nervous system modification bolted directly into someone’s brain stem and spine that when active sends them into a hyper aware, hyper reactive state experienced as time slowing down. Out of everything that would probably fry someone’s brain pretty directly.