The current go implementation of Fchmodat has some workarounds since the flags argument on Linux is ignored:

flags can be 0 or AT_SYMLINK_NOFOLLOW for POSIX

func Fchmodat(dirfd int, path string, mode uint32, flags int) (err error) {
	// Linux fchmodat doesn't support the flags parameter. Mimick glibc's behavior
	// and check the flags. Otherwise the mode would be applied to the symlink
	// destination which is not what the user expects.
	if flags&^AT_SYMLINK_NOFOLLOW != 0 {
		return EINVAL
	} else if flags&AT_SYMLINK_NOFOLLOW != 0 {
		return EOPNOTSUPP
	}
	return fchmodat(dirfd, path, mode)
}

There is a proposed patch that creates a new version of this syscall (fchmodat2) that handles the posix flag AT_SYMLINK_NOFOLLOW properly at the kernel level.

When made accessible in the release kernel, library implementations will be able to utilize it for their fchmodat() implementation, circumventing the need for existing workarounds.