(tl;dr you are confusing symptoms of a disorder with its root cause. See evidence below.)
I don't understand, are you suggesting that overconsumption / overstimulation behavior is / could be the cause of ADHD?
Because they certainly are effects and symptoms (not root cause) of ADHD, this is a well established fact, kind of core part of ADHD literature and research, actually... (I mean: dysregulation of dopamine; impulse control (lack thereof); higher substance abuse risk (esp. when unmedicated)).
While excessive screen time or poor diet can exacerbate executive dysfunction or poor sleep in any human (esp. child), they do not create the neurodevelopmental deficits that define ADHD. Taking away a video game does not repair a child's dopamine transporters.
I feel there is enough literature to substantiate this. I'm interested in this because I have a clinical diagnosis of ADHD which I got only in adulthood, but better later than never; getting the diagnosis has absolutely helped me in life, in various respects.
By the way: I recognize that in certain countries, ADHD may be overdiagnosed (idk, though); medications overprescribed (again, idk, but acknowledging the risk here; not here in Baltics (LT) though, I think);
AND - what ruffles my jimmies PARTICULARLY - prevalent overuse of ADHD term and culture of (over)self-diagnosis of ADHD in social media and elsewhere (general culture, too; I hate that so much, I believe it contributes to such one-sided unscientific docs as well as not-scientifically-grounded viewpoints).
Those over-self-diagnosing people really do not help the rest of us, to put it mildly.
As for canonical evidence and studies:
1. The World Federation of ADHD International Consensus Statement: 208 Evidence-based conclusions about the disorder (Faraone et al., 2021) - https://pubmed.ncbi.nlm.nih.gov/33549739/
2. Dr. Nora Volkow's dopamine research (e.g. JAMA, 2009) - https://jamanetwork.com/journals/jama/fullarticle/184547
3. Dr. Russell Barkley's Theory of Behavioral Inhibition (see e.g. his long talk directed towards parents of ADHD children, if curious; on youtube)