It isn't that it's not true, it is! Social media sucks for mental health. It's just also true that there are many legitimate reasons to be upset. I say this as a 24 year old that has been very very lucky to have affluent parents and gone to a good university and gotten a good job. I make more money than I honestly think anyone needs at my current cost of living and yet despite this I have so many friends that are barely scraping by.
Depending on what stats you go by, the average American household couldn't spare a $400 expense: https://www.fool.com/retirement/2018/05/23/guess-how-many-am... That's a fucking Playstation. That's absurd.
So sum the constant anxiety of basically no economic safety net, climate change (which is looking to be "how bad", not "if"), social media reminding you of these AND how much better your friends are doing.. Is it any wonder everybody feels like shit?