Prostitution in the US is only legal in one state, Nevada.
Even then, it’s only legal in some parts of the state.
I don’t think sex work should be illegal. It’s mostly illegal because the USA never fully recovered from the Second Great Awakening. Before that, sex work was generally legal.
That still doesn’t deal with the incel problem. Legal sex work would help some of them, but the grievance with most of them is that women offer it to other guys for free but keep it away from them. That seems like an impossible issue to address.
There are also things unique to American culture that makes it create its own monsters. We basically deal with it the same way we deal with our obesity epidemic and our homelessness problem, which is shaming them and lecturing them about personal responsibility. It’s ineffective, and in the case of the incels, all it does is drive more hopelessly single men to those online safe spaces where they become radicalized.