nmtui is just a console UI for NetworkManager. Similar UI is most likely provided by your desktop environment of choice as well. It has nothing to do with iptables.
"Not up to date" is putting it mildly, idk if there is anything in nag2 that's still relevant these days; I get the feeling that it will just confuse more than inform at this point unless you already know the stuff and history.
Not sure what exactly are you asking about. iptables/nftables is an interface for in-kernel packet filters. NetworkManager... well, manages your interfaces and connections. systemd-resolved/dnsmasq handle DNS. They mostly just do their own thing, with NM sometimes using the other ones as needed (for example, it will set forwarding rules up and run dnsmasq when you choose a "Shared to other computers" option in NM).
