These authors have big Google Docs of evidence, https://jonathanhaidt.com/reviews/. But if you read it, you will see the effect is (AFAICT) limited to certain populations. There is a significant fraction of students that do have trouble with executive function and staying on task and will fail to do their homework because of social media access. Then there are the other students that have no trouble staying off social media when they have to do homework.
Part of this is because the pre-frontal cortex (associated with logic, will power, discipline, focus, etc) doesn't finish developing until about age 25.
Until then, folks can be reliant on the adults in their environments older than that age, if they haven't built up some abilities.
