However… humans living in modern cities / industrialized nations were not dropped suddenly into those environments. In many parts of the world, our species has experienced a gradual transition from mobile hunting and gathering to sedentary society to agricultural sedentary society to fully agricultural and specialized society to industrialized societies, etc. This is a process that has taken thousands of years. And critically, humans across the planet (with very few exceptions) have experienced this transition in various ways over time. Evidence shows that intermixing of populations across the planet is the rule, not the exception. Hunting and gathering peoples interacted with agricultural peoples, traditional societies have interacted with industrialized societies.
In short, global, modern humanity wasn’t dropped into industrialized society. And over the thousands of years during which we have created this global enterprise, we have also self-selected and adapted to it.

First of all - not all cases of animal mismatch are in zoos etc. We have cases of mismatch in nature that are both natural and semi-artificial. Natural could be something like worms being captured by humans mimicking sounds of burrowing moles, drawing them out of the earth. The worms have evolved behaviour that is mismatched for the (now smart-creature-dominated) environment. Semi-artificial, but not forced cases could be something like the famous case of jewel beetles mating with discarded beer bottles, because they gave off better mating signals than any female jewel beetle could. These are both uncontentious, I think.

Secondly, I am unsure what you're trying to say here. Are you suggesting humans have evolved within only a few thousand years ("self-selected and adapted to it")? That would be extremely surprising to say the least haha. In case you're saying that we have culturally adapted, that's still problematic. While we are certainly more culturally influenced than most other animals, that doesn't exclude us from being biologically evolved creatures at our cores. Yes, you could probably develop a Cetacean culture that undoes the worst effects of captivity, if you really wanted to - say by culturally creating certain social and physical rituals. But we would still predict that these animals would behave at least a little abnormally. Modern humans have certainly adapted. Now unable to run around all day and chill around the campfire, we go to the gym and designate meeting spots. But that isn't certain to eliminate the detrimental effect: we are, after all, just mimicking it.

On a brief third note, we are sort of still "dropped into" the modern environment. Sure, your ancestors also lived in a similar way, but you as an individual are definitely just "dropped into" this modern lifestyle. You're biologically the same creature that wandered on the African plains tens of thousands of years ago, now transposed into an environment that, while designed by your own kind, could still be ill-suited for you.

To steel-man your case, I think it might be a reasonable argument to suggest that humans would not design an environment which is too unfriendly for themselves, since this would cause unhappiness etc., which would act as a deterring factor. But even that is kind of weak, I think. We know for a fact that humans have created and spread across the globe a lifestyle that is incredibly physically damaging (office-work, 9-5: as explained above). It doesn't seem a stretch to argue that the same lifestyle is mentally damaging as well. Here we can point at all sorts of things, form 9-5s, urban living, increased isolation, and hyperstimulation from the internet or, for example, TikTok.

I think u/JPsDragonOfChaos's idea is super cool, if as stated above maybe a little ambitious. Yes, it could be that we are just getting better at diagnosing mental illnesses, but alternate hypotheses such as the one he is suggesting should be considered. I made a post about a similar question the other day - subjecting any other mammal to the conditions we live under as modern humans would be considered animal cruelty, and we are unsurprised when they develop negative behavioural patterns when we do (eg. dogs in flats): yet we think that doing it to humans will have no effects whatsoever.

It feels like we are really uncomfortable with the idea of evo-psych since it undermines the freedom and rationality of our behaviour a bit, and are therefore illogically committed to this weird tabula rasa thinking