There are definitely activities that have been shown to increase IQ, even when attempting to correct for confounders, although not by a dramatic amount.
For example, spending an additional year in school increases IQ by 1-5 points, depending on which study you believe. [0] Similarly, having a healthy diet as a child "increases" IQ, although you could equivalently phrase it as malnutrition decreasing IQ.
[0] https://www.psychologytoday.com/us/blog/brainstorm/201806/ho...
The three study types respectively yielded estimated IQ increases of approximately one point, two points, and five points per additional year of schooling.
And what were the three study types?
Cognitive tests were taken before participants differed in their degree of education (e.g., before some dropped out of high school) and again afterward, sometimes decades later.
A policy change, such as an increase in the mandatory education level, resulted in some students staying in school for longer.
Students who made an age cutoff to begin schooling were compared with students who had not.
So the best study, which tested IQ scores before and after, showed the least improvement, at 1 IQ point. Not exactly a ringing endorsement of education for boosting IQ. I would conclude the opposite of this article. When better studies show smaller and smaller effect sizes that’s a good indicator that there’s probably nothing going on.