There are text versions for FW software that can be configured via shell.
UFW is popular one I believe:
pi@ph5:~ $ apt show ufw
[..]
Description: program for managing a Netfilter firewall
The Uncomplicated FireWall is a front-end for iptables, to make managing a
Netfilter firewall easier. It provides a command line interface with syntax
similar to OpenBSD's Packet Filter. It is particularly well-suited as a
host-based firewall.
And the only time you need to enter iptables MASQUERADE and iptables-persistent on the Bash shell is if want to route one network to another.
Examples plenty on the net like in that other posting bout Wifi sharing.
I takes 5 seconds before it is launched instead of one of the first PIDs. Dnsmasq for example was always around ~600. Pihole is about ~1300. Anyone, no problem for me.
The title is indeed correct lol NM does indeed break pi-hole in a specific situation (sharing connections).
Thank you again for the help @deHakkelaar Eet smakelijk