The remaining 10% are major psychological disorders that science still has no answers for.
https://ourworldindata.org/urbanization
https://www.weforum.org/agenda/2020/11/global-continent-urba...
I don't disagree that sunshine, healthy foods, etc. can help, but to not only say that "90%" of mental health issues could be resolved by just going outside (hint: >10% are impacted by non-environmental mental health conditions which require medication, such as bipolar, schizophrenia, ...). And "10%" we have no idea what to do with? Eh, just ignorance all around.
This isn't reddit. Do research.
I don't believe that anything in Psy* industry has any relation to Science. Those problems listed here can be easily cured by Philosophy. For example, what is schizophrenia, is this the gray matter damage? The white matter damage? Nobody knows because Psychiatry is 100% about obeying the government masquerading as a Medicine.