I think you would have heard about a lot more “cold-fog” if that was the case for cognitive issues. I am sure it does happen—covid and the common cold are both coronaviruses after all, but I’ve been hearing numbers as high as 30% with covid:

https://www.nationalgeographic.com/science/article/how-does-...

With that said, I am sure if we poured this much research into other severe illnesses we would find out a lot more bad news about what they do to our bodies…