MSVC support for C is fairly terrible. For the projects we write that are portable to Windows we insist you use GCC or Clang on Windows. No one has time to deal with the lack of even standard C1x/C2x features (never mind useful extensions like attribute cleanup).

Surprised about FreeBSD. My experience is that porting Linux software is usually pretty easy as long as it's not using some Linux-only feature (io_uring for instance).