Build dense housing. Eliminate local code and zoning regulations that prevent the construction of dense housing (parking mandates, for instance). Provide "housing first" support to homeless people.

More complicated answer: we already have the resources, technology, and knowledge required to end homelessness in the US. The reason we haven't is that we don't want to. Few politicians are willing to say it, but homelessness is part of our economic model. Our economic targets for things like housing prices, unemployment, etc. make homelessness inevitable - and that's how capitalism is supposed to work according to liberals (which includes both Democrats and Republicans). In capitalism, access to living necessities must be restricted in order to coerce labor and increase productivity.