The data we have on bans on underage drinking and smoking show that they work. Some kids will still smoke and drink, but the number is reduced, drunk driving accidents go down, and eventually fewer adults abuse alcohol and smoke cigarettes.
The myth about age limits making it forbidden and attracting more kids to do it is just that it’s a myth. Spend some time looking at the studies. They almost universally show that age limits on drinking and smoking are harm reducing.
Second, the peer pressure to drink/smoke has never been as strong as the network effect of social media. Almost all 15-year-olds are on some form of social media, I don't think you can reasonably expect they will suddenly stop wanting to socialise outside school. Their entire identities are built around their online presence; that was never the case with smoking or drinking, at least not on this scale.
I'm sure it will have some effect, but kids are clever, and they have lots of time, they will find ways to bypass these fairly weak bans. Imo, the only way to do this is to provide an alternative along with the ban, like what the Russians are doing with Max as a replacement for Telegram/WhatsApp, though that's not entirely successful either.
Then there’s the contrast between calls for regulating social media for kids followed by the outrage when people realize that 1) products they use are considered social media (Discord, Reddit, Hacker News) and 2) you can’t keep kids out without age checking everyone who uses the product.
sure, just like some kids sneak cigarettes; but the vast majority don't. I disagree that it's symbolic.