I did not read the study, but the finding seems trivial and limited at the same time: Anything you do to alleviate or prevent boredom that is not creative can be said to 'prevent reaping creative rewards' of boredom. Not just social media (or any media consumption, really) but also sports or calling a friend or helping in a soup kitchen. If you didn't do it, you'd feel boredom, and might pick up something creative in…
This is no doubt true but smart phones basically give you the option to never be bored, and get instant gratification whenever you feel like it. I don’t think it is limited to social media but I imagine there are pretty profound consequences to that.
Is it true though ?
I have the feeling people say this the same way they assume living in a high population density area gives you option to never be lonely.
I’d argue having stuff to read/watch is orthogonal to being bored, it’s not a state of mind you can fill with any random crap in your feed.