I think the GP meant that quantum theory and relativity are incompatible and thus both cannot be exactly correct at the same time. Not referring to quantum vs classical.
0. Special Relativity is already baked into the Standard Model, which is a quantum theory. It's General Relativity that causes problems.
But as a physicist I have no illusion that any of our theories are actually true. They are all models that help us making sense of an unimaginably complex universe.