I fully believe that COVID can and does cause brain fog and cognitive loss, but when it comes to test scores, how can learning loss from lockdowns be ruled out as a cause?
Just because in-person learning resumed at some point doesn't mean that the previous year(s) of remote learning didn't negatively impact kids. Each school year tends to build on the knowledge taught in the previous school year. If the kids taking the ACT now were freshmen at the start of the pandemic and had to suffer through remote learning for a year or more (I'm not actually sure how long most schools were doing remote), wouldn't we expect the poorer learning during their early high school years to lead to poorer ACT test scores now?
I suspect that it's probably a combination of effects from both remote learning and covid brain fog. And I anticipate that we as a society will be feeling the effects of a generally worse off Gen Z for many years to come.