See this recent documentary by KOMO News in Seattle about their problems, which are pretty similar to Portland's, SF's, LA's and a lot of other major cities with larger homeless populations. Crime is soaring. Most are homeless due to drug addiction. Until that part is solved and they can think clearly and rationalize normally again, giving them cash will likely only fuel the problem and keep them right where they're at. And with everyone walking around with $50k cash in their pocket, because they don't have bank accounts, crime would be even more rampant as they steal it from each other.
I don't really buy that money would fuel the problem, is there any study that indicates that? They'd still be drug addicts, but they'd be more comfortable, well fed drug addicts which makes things better for everyone.
If anything I think money for a place, clean clothes, and food would make it much easier to get off drugs.
Anyway, saying it's a mental health problem is really reductive. Plenty of people with the same problems aren't homeless; some of these people can potentially dig themselves out if given a chance, most importantly a place to live.
Unfortunately I don't believe something like that is practical unless it's done on a national level.