Disclaimer: I myself have never applied for disability, but my career in disability services has me interact with a lot of folk who are on SSDI.
In the United States, to get on disability, regardless of your diagnosis, you have to prove that this diagnosis impacts you in such a way that makes it impossible for you to do ANY sort of gainful employment.
Most people I know of who get disability and who have mental health issues either A. also have autism or another neurodivergence, or B. also have a physical issue of some kind. It is possible to get on disability with just a mental health condition, but to prove that said mental health condition makes it impossible for you to do any job, it often takes a lot of doctor documentation, often from impatient facilities if that's applicable. It also "helps" in this regard if you have a resume full of failed jobs -- if you've had 10 jobs in the past year and none lasted more than a month, for example, that does demonstrate that you've tried work and that work isn't a feasible thing for you.
That said, most people who apply for disability for mental health conditions are denied the first time and often have to appeal, sometimes twice or more, obtaining even more documentation from doctors, vocational rehab, whoever may help (if you had mental health issues in school and have the school documentation to prove it, that can also help). Having access to a lawyer to help with the appeal also helps -- some areas have agencies that offer a certain number of pro-bono cases to this end.
The pay is often significantly lower than the cost of living, but being on SSDI or SSI does often qualify you for food stamps, Medicaid/Medicare, utility assistance, and maybe even rental assistance, depending on which state you live in. Most people who live on SSDI/SSI alone are struggling, but it can keep you out of homelessness if you otherwise have NO income coming in.
