Gen Z is the first generation in a century to show a general IQ less than the previous generation, in their case, Millennials. The neuroscientist who presented those findings hypothesized that it's due to increased screen time, though whether he meant screen time as children, or screen time currently, I don't know.
As with all studies, it probably needs to be replicated a number of times. Don't know if that's been done, or is planned to be done.
Also, it's a broad-brush finding. I bet if you read the fine print found in most published research, it will say somewhere near the end "A lot more research is needed."
Popularizers and summarizers tend to say "Study finds that...." Almost always, when I've read papers for myself, their "conclusions" are much more modest and they go out of their way to say "don't read too much into this."
