That's a combination of
(a) a relatively modern myth ("It was always that way"),
(b) a cherry-picking from millenia for instances where that did happen (which wasn't "always" - many periods, even for centuries on end, had almost no change between generations regarding lifestyles. For some rural places that was even true for millenia.).
(c) from the cherry-picked cases where it did happen, ignoring the subset that it was also a totally valid criticism (e.g. in the decline of golden-era Athens or the fall of Rome, or the Weimar Republic), when the change in culture and attitudes eventually killed the community/city/republic.
Many of the instances where we have records of this being a recurring complaint of adults toward the youth were in those times of little apparent lifestyle change; part of that ia that the distance of our perspective probably minimizes changes that were perceived as significant in the local context, but a bigger part is that, while objective changes in lifestyle or technology can provide something to tie the complaint to, the main driver of the complaint is not the change in society but the change in the observer’s position and perspective within society.
But yes, the youth is always terrible. I've read that in the Hagakure, but I think it has already been mentioned/been a "fact" in ancient Greece, too. ;-)
But...that’s how older generations have always responded to what younger people do for social approval, and older people interpreting what they see that way as a precipitous decline since their own youth is one of the oldest clichés possibly as old as civilization.
> I find it hard to believe that there's "little association" when things don't go as planned.
Maybe, but maybe that is just as true independent of digital engagement.