However, even if you go to the extreme of not using any features that require runtime support, if you are using hosted C++, in practice you still have one bit of runtime: the entrypoint. Technically, an operating system could implement the bits that call main, but to the best of my knowledge none of them ever have. So every compiled binary from every hosted C++ implementation begins at the runtime library. (Admittedly, normally the C runtime library, since C++ doesn’t differ here, but that is just another layer deep of pedantics. In practice, everyone has a runtime.)

Nitpick: As far as I am aware OpenMP is not part of the language itself but an extension. But yeah, you could argue that is runtime scheduling in C++, I think.