"AllowedIPs" detemines which target networks are allowed to be routed through the tunnel. If it actually gets routed or not depends on the software. wg-quick ad

"AllowedIPs" detemines which target networks are allowed to be routed through the tunnel. If it actually gets routed or not depends on the software. wg-quick adds routes to AllowedIPs by default, systemd-networkd does not.