Currently iptables does not work out of the box on Librem5 chestnut phone with PureOS.
root@pietro:~# uname -r
5.3.0-librem5-h1
root@pietro:~# iptables -L -n -v
iptables: Operation not supported.
I had to modprobe iptable_filter then iptable said that I have to use iptables_legacy