Im sure smartphones could be a possible factor however one must not forget how depressing the whole high school experience is. I think that the pressure has increased quite a bit. The amount of hw has also increased. I don’t think that this suicide increase has been observed in say Finland.
When I was a kid you can make an idiot of yourself and nothing would happen. People would see and they may make fun of you, but that was it.
Now if you choose to make a fool of yourself (or do it accidentally) you may get your picture taken/video made and now there’s proof forever to show other people. And it can be posted online. Where people on Reddit or something else will vote it up and share it.
I imagine there’s a level of self censorship and self-consciousness the previous generations never had to apply to themselves. Having that kind of low level stress around all the time can’t be great.
And that’s not including any pressure to look GOOD on pictures taken of you/taken by you.