The creation of, or edits to, the .config file within the root of the kernel source tree via make menuconfig or other methods is not the final step in how the kbuild system works with the configuration. No, it now proceeds to internally invoke a target called syncconfig, which was earlier (mis)named silentoldconfig. This target has kbuild generate a few header files that are further used in the setup to build the kernel. These files include some meta headers under include/config, as well as the include/generated/autoconf.h header file, which stores the kernel config as C macros, thus enabling both the kernel Makefile(s) and kernel code to make decisions based on whether or not a kernel feature is available.
Moving along, what if you are looking for a particular kernel configuration option but are having difficulty spotting it? No problem, the menuconfig UI system has a Search Configuration Parameter feature. Just as with the famous vi(1) editor, press the / ...