Whether to enable nftables and use nftables based firewall if enabled. nftables is a Linux-based packet filtering framework intended to replace frameworks like iptables.
Note that if you have Docker enabled you will not be able to use nftables without intervention. Docker uses iptables internally to setup NAT for containers. This module disables the ip_tables kernel module, however Docker automatically loads the module. Please see https://github.com/NixOS/nixpkgs/issues/24318#issuecomment-289216273 for more information.
There are other programs that use iptables internally too, such as libvirt. For information on how the two firewalls interact, see https://wiki.nftables.org/wiki-nftables/index.php/Troubleshooting#Question_4._How_do_nftables_and_iptables_interact_when_used_on_the_same_system.3F.