Decent, long-term medical facilities.
The problem is that solution is expensive. It's way cheaper to simply move the problem somewhere else (jail, different neighborhood, etc.) than fix it.
In addition, it has odd failure modes. You want to create a cluster of people to amortize the healthcare costs. However, your treatment options generally want your homeless to be separated as much as possible. The standard treatment for drug addiction generally starts by separating the patient from those who also do drugs or who provide access to drugs, for example.
The reason we don't house the homeless is a percentage of them destroy whatever is given to them. So, use the treatment process to get them well first.
https://www.theguardian.com/cities/2019/jun/03/its-a-miracle...
Stable independent living only matters once a person is sober and sane enough to use it.