most of the studies showing superiority of keto over other healthy diets for cognitive health are very poorly done.

I think people want a quick bullet. The point in the article have been confirmed by thousands of studies:

Eat a balanced diet (whatever is right for you; low carb MAY be best for some; low fat for others)

Exercise mind and body regularly (particularly the mind, in terms of cognitive slowing)

regular contact with others

no drinking or smoking (or not drinking too much)