Install the package for the interfaces. Configure your stuff at /etc/network/interfaces
apt install ifupdown
Start the networking service
ifdown --force enp0s3 lo && ifup -a systemctl unmask networking systemctl enable networking systemctl restart networking
F*ck netplan and systemd networking in the butt
systemctl stop systemd-networkd.socket systemd-networkd networkd-dispatcher systemd-networkd-wait-online systemctl disable systemd-networkd.socket systemd-networkd networkd-dispatcher systemd-networkd-wait-online systemctl mask systemd-networkd.socket systemd-networkd networkd-dispatcher systemd-networkd-wait-online apt-get --assume-yes purge nplan netplan.io
Source: https://tweenpath.net/ubuntu-18-04-disable-netplan-switch-networking-etc-network-interfaces/