Latest iptables 1.8.3 was supposed to be a minor/bug fix release, ended up wih .so changes, which will make the system unbootable (kernel panic). It is now removed from the [build] repo.
Make sure to install core/iptables 1.8.2 prior to rebooting. Or if your mirror is synced, run pacman -Suu after updating.
If you ended up here looking for answers for an unbootable system, use the chroot doc:
and install iptables 1.8.2 in the chroot.