FOCUS is wrong. did you mean CAP_PROP_FOURCC?
could you show the Python code that gives you 120 fps?
how does the performance differ if you leave various set() calls out of the program?
what’s the version of the OpenCV you’re using from Python? what’s the version you’re using from C++?
are both running on the same system? does any of them run in a VM or other virtualization/containerization?