Ok then. If we take the hypothesis at face value, what is to be done about it? Prohibition obviously isn't a solution as that's the status quo - it's already illegal for teens to buy and consume cannabis.
Otherwise, we don't have to completely deregulate sale and use. Legally limit THC concentration, and/or require a certain minimum for the CBD-to-THC ratio in products. As the article (and others here) have pointed out, THC concentration has only gone up over time, especially as pot has become legalized in many places.
Certainly some people will still find/make things with higher concentrations, but legally limiting the concentration will act as education of its own, and a lot of people will end up with safer products.
Education is an idea, let people know what the risks are and what symptons are to go see a doctor. This could be a mandatory magazine at shops.
People at risk could get better treatment, just someone to talk to about their strugles in life can be very helpful.
Ignoring that these are teenagers that are going to do whatever they want because that's what a teenager does just means that you're going to waste your time.
They've started to put the above statement on top of cigarette cases at my local grocery store. It's not super prominent, nor is its color garish but I'm still surprised every time I read it and I've seen a few others surprised too. There are certainly ways to effectively use reading material to combat these things.
If the goal is preventing severe mental illness, then the best solution we've got right now is coordinated and well-funded multi-agency intervention to support at-risk families and young people.