Here's my pet hypothesis (that has zero backing that I'm aware of) regarding the increase* in mental health issues:

When our parents, their grandparents, etc, grew up, they all broke a metaphorical bone (the metaphor being some sort of trauma). Maybe their parents beat them or ignored them, maybe they had undiagnosed conditions, etc. And this has been the norm for no one knows how long. And part of that norm was never treating it. It was the norm. So like an untreated broken bone, it was really obvious that something's busted, but since literally everyone had a fucked up bone sticking out, no one thought it strange.

Along comes some mental healthcare. Some few people embraced it and had the bone broken and reset. Hoo buddy did it suck, but was ultimately a good thing. Now they can reach the box of cereal on top of the fridge with either hand. More, they could do things they had completely ignored because their previously broken bone prevented them from doing so. And so these people realize that the norm of broken bones is shit. They go on to encourage others to have their bones fixed, though that's a bit of a non-starter. Now they are the weird ones for not having broken bones.

More effective is this message with the younger generation. "Don't accept broken bones, get treated immediately". And they listen to their elders as they are taught and they get treatment. Now, this is kinda new, actually addressing issues as they come up instead of just walking it off. There is some calibration space that needs to happen (looks at the rise and over prescription of ADHD meds when I was a kid). But less than you think, because broken bones are so common that everyone in history has had at least one.

Now, when the older generation tells them to walk it off, they balk and say that that's dumb because, largely, it is. And there isn't a nice measure of severity that exists. You only know how painful your broken bone is and it doesn't happen enough to give perspective on the variety in general. To say nothing of some people's broken bone affecting how they feel said bone (I experience alexithymia). So the younger generation does their best at assessing their broken bone because mental healthcare is pretty garbage since (among a lot of other things) it hasn't scaled to a population that all wants it. And the older generation controls the purse strings and mental healthcare can't expand because the people with the money think we should all walk it off (glad I could work this into a low-grade indictment of capitalism).

Obviously there are many other factors (lead poisoning, microplastics, looming environmental apocalypse for starters), but this is my extremely poorly sourced hypothesis. Not a theory, hypothesis.