i.e. delete your facebook, your tiktok, your youtube and return to calling people on your flip phone and writing letters

That sounds like an abstinence-type approach. Not saying that it's not a valid option (and it can be the only effective option in case of a severe addiction), but it's certainly not the only way that could work. Put simply, you don't have to give up on modern technology just because they pose some dangers (but you totally can, if you want to, of course).

I can personally vouch for just remembering to ask myself "what I'm currently doing, how I'm feeling right now, and what do I want?" when I notice I'm mindlessly scrolling some online feeds. Just realizing that I'm bored so much I'm willing to figuratively dumpster-dive in hope of stumbling upon something interesting (and there's nothing fundamentally wrong with this, but I must be aware that this interesting thing will be very brief by design, so unless I'm just looking for inspiration and then moving somewhere else, I'm not really doing anything to alleviate my boredom) can be quite empowering. ;-)

all the social networking on smart phones has not been a net positive in most people's lives

Why do you think so? I'm not disagreeing, but asking because I know plenty of individual examples, but I'm personally not feeling comfortable enough to make it generalization (because it's hard) and wonder what makes you do.