It's not a great study. It's observational, and the best it can show is correlation. It's just as likely that people with that score lower on cognitive tests are more likely to get covid, which doesn't seem unrealistic. A bit of armchair analysis (with only a little bit of ax-grinding): https://sebastianrushworth.com/2021/07/26/does-covid-cause-brain-damage/
It's not a great study. It's observational, and the best it can show is correlation. It's just as likely that people with that score lower on cognitive tests are more likely to get covid, which doesn't seem unrealistic. A bit of armchair analysis (with only a little bit of ax-grinding): https://sebastianrushworth.com/2021/07/26/does-covid-cause-brain-damage/