The recent rise in home-schooling, and anti-intellectualism probably aren't helping much either, especially when you see things floating about here and there about how schools are hell-bent on brainwashing your children, and you should pull them out lest they be exposed to communism and the moral degradation of society or some such.

COVID does seem to be a part of it, but not all of it, since some of the data linked in the article shows a small decline in the scores before the pandemic and lockdowns. They could well have just exacerbated the underlying issues.