Idk but in France, when I was still a teenager, it was not that uncommon to talk/joke about the fact that we will never be able to retire. In high school, most of my classmate already started to have a political conscience and where thinking about this kind of stuff. Same with the environment.
We already had social media at the time (mostly facebook) and yes, I won't deny that there was already something anxious about feeling pressured to always show yourself/self yourself to other. When I look at Instagram today, I feel like it got even worse.
But, as someone still under their 30's, I think we shouldn't also deny what the original commenter said. In the case of Europe (and in my case France), we have seen the come back of extreme conservatism in politics, the slow decay of our public services, the inability for politician to make important decision for the environment, the idea that we will never retire/have a pension (which is not necessarily true but is definitely a strong belief), the imbalance in wealth creeping higher and higher every year, home ownership becoming harder and harder ...
Whereas the generation of my parent (those from the 60's-70's) had, in general, a more positive/peaceful outlook on the future, I find that my generation and those younger that me tend to be more skeptical, if not negative.
I really think that the current mental health issues are a combination of multiple factors and that social media is just one (but maybe a big one) of those factor.