the key to solving homelessness is not affordable housing, regulation or vast amounts of spending or even UBI. The answer is UBL ==> Universal basic Land. It's the idea that every person should have some means of having some land and being allowed to build on it. maybe not in downtown, maybe not any specific area, but at least somewhere. you can't just tell people to whole up in a homeless shelter. I found out that the life expectency of the average homeless person is in their 40s, Yikes! there should be someplace for everyone on this planet. give people some land, or let them buy it for a relatively reasonable amount and don't charge them rent (property taxes), at least for up to a certain value (say the first 50K or 100k). Once you have land, and freedom to build on it, you can build your home or have a construction company do it for you, in a way that's cost effective.
Even the native american indians and countless others in the global south with far less income per capita had/have homes. It shouldn't be so hard: the problem is land use policy and regulations.