This is not worthy of an existential crisis. It's worthy of concern, but not a ZOMG freakout. You have to keep in mind that "IQ" is not a robust metric. Lack of sleep blows big holes in performance on standardized tests. Distraction is worse. Any sort of infection can lower IQ. COVID-19 infection does cause measurable gray matter reduction. But then, so does drinking. I'm not a fan of gray matter reduction, but most of these studies pretty much say debilitating disease is debilitating Which should hardly be surprising. Now - is that debilitation permanent? Transitory? Profound? Trivial? Well again, it's a "novel" coronavirus which doesn't mean "exciting and fun" it means "new under the sun" and we're still deep in the fog of war. Get vaccinated. Helps.