Compiler can sometimes inline syscall wrappers, so not that easy to check statically. For the same reason searching for SVC instructions would yield tons of results. If you search for the exact syscall ID moved into X16 you’d find it immediately.
The stable interface to syscalls on Apple platforms is libSystem, which is a dynamic library. Compilers cannot inline syscalls on Apple platforms as that would defeat the whole point of making libSystem the stable ABI. In fact, compilers don't even see libSystem itself when linking, they just see a .tbd file that lists all of libSystem's symbols.