There is no longer any controversy among credible medical researchers that Covid causes clinically significant harm to the nervous system, including brain damage, cognitive impairment, dramatically increased risk of various neurodegenerative diseases and mental health conditions, and so on.
Like everything else, this neurological damage (and associated risk) is cumulative with repeated infections.
Current research in this field explores prevalence, severity, mechanism, and possible treatment avenues, as authors at this point have an unassailable body of prior research they can cite in the preamble to establish the fact of said damage.