Setup network via /etc/network/interfaces/


I need some help.

On debian, Freepbx 17 firewall and network admin are only working with the old way to setup network : /etc/network/interfaces/

how to switch back in a sure way from standard systemd.networkd & netplan to the former setup ?
Running on a VPS, always keeping network on is mandatory

NB: distro version 6 is using files in /etc/sysconfig/network-scripts easily managed with nmtui.