OpenMP support is baked into many compilers including GCC and LLVM: https://www.openmp.org/resources/openmp-compilers-tools/

It is enabled by setting compiler and linker flags, rather than INCLUDEPATH. The Qt Creator code model should look for these flags and update its own search paths accordingly.

The attached code and screenshot shows that the code builds and runs fine, but the Clang code model (both libclang and clangd) doesn't recognize OpenMP.