“The study, published in the journal Intelligence, used an online, survey-style personality test called the Synthetic Aperture Personality Assessment Project to analyze nearly 400,000 Americans.”
The headline says proving. The data is an online personality survey from 2006 to 2018, not an IQ test. Three of four domains fell and spatial reasoning went up. One of the study’s own authors says the results do not mean anyone’s mental ability got lower, and the headline ran anyway.