Wake on LAN (WOL) for Ubuntu 20
dito Proxmox but with orhter path for ethtool:

nano /etc/systemd/system/wol.service

[Unit]
Description=Wake-on-LAN for <interface id>
Requires=network.target
After=network.target
[Service]
ExecStart=/sbin/ethtool -s <interface id> wol g
ExecStop=/sbin/ethtool -s <interface id> wol g
[Install]
WantedBy=multi-user.target

systemctl start wol.service
systemctl enable wol.service
systemctl is-enabled wol.service
systemctl daemon-reload

Wake on LAN (WOL) for Ubuntu 18 (Bionic)

On a server without GUI = with “Netplan” and without “Network-manager”
https://askubuntu.com/questions/1053302/wake-on-lan-not-working-if-i-turn-of-with-ubuntu