Spending money is necessary but not sufficient to fix this sort (or literally any sort?) of big problem.

I hope you don't think San Francisco having spent a lot of money on the problem (the $100k per person figure in isolation is deceptive, but let's not dwell on that) means we've expended more than a really minimal amount of effort as a nation on the problem. Consider how little the problem of homelessness was discussed during the last presidential cycle, or how often it's discussed in congress, and I think you'll see what I mean. (consider the words used when debating it and you'll really understand what I mean)

Just because you can spend money poorly doesn’t mean money isn’t needed to fix an issue.

Something to keep in mind is that that figure includes homeless people who have been homed and are being supported, it's not just the ones currently on the streets.

And still once I was ina small restaurant that let a homeless guy use the toilet and they forced the door open after hearing crashing sounds, and he had painted the walls with his poop and jumped up and down on the sink until it broke off.

Days later I saw a sign in their window saying the bathroom was for customers only.

The problem is money, but for preventing homelessness and mental illness in the first place.

What do you suggest the solution is?

I assure you, if they stopped spending that money tomorrow, things would get dramatically worse, as all the people that money keeps off the streets would be on them.