It's quite possible that the causality goes the other direction, and a baseline population of brain disorders is being ascribed to the last notable thing that happened to them (which has also happened to ~ the entire population at this point).
It is not plausible to propose that 69-96% of patients, including children, had undetected brain disorders and that was the direction of causality.
If they’re only testing people with symptoms, the causality could easily go either way.
These are participants whose health is being followed long term. They had brain scans before and after COVID, and abnormalities were detected in the scans post-COVID.