Shoot me down for my opinion, but my logic tells me that there may at least be a contributing factor in it. Other contributors being mad woke ideology, head meds, insane childhood vaccine program, the industrial school system.... so many things wrong with the development environment of many many Americans. The games alone are not the problem, or these shootings would be prevalent all over the world. They're not. It is almost a uniquely American thing. One thing we know for sure is that Americans are by far the most medicated people on the planet.
Discussion
The video games causing violent crime has been a common trope going back 30 years now, and like you said it's not that way in other countries. I'm Canadian, and I'd say we have a fairly similar landscape for schooling, vaccines & medication, and ideological issues. Notably, Canada and the US are two of the countries with the highest use of anti depressants, Canada having a slight lead, 16% vs 13% in the US.
I was looking at the stats for murders, comparing Provo to the city I live in. Similar population, just above 100K. As far as gun ownership goes, about 45% of household in Provo have guns, compared to 40% in my province. Provo has a relatively low crime rate compared to the US average, and since 2010 has had 20 murders. In my city the last murder was in 2006. The previous murder was about 20 years before that.
On a national scale America has about 3x the murders of Canada, 5.9 per 100k vs 1.9 per 100k (2023). I'm not sure what accounts for the difference.
Yes, there are so many confounding factors, and some of those school shootings may even have been staged. Nothing is beyond possibility in the US.