So first you would want to convert your LAN interface on your laptop to a bridge:
See https://netplan.io/examples#configuring-network-bridges
Then once you have a network bridge, you can replace the existing NIC in your container with one connected to your bridge using:
lxc config device add <container> eth0 nic nictype=bridged parent=<bridge interface name>
Note: You said you were on wifi, I am not certain, but there may be issues with bridging onto a wifi network due to the way wifi uses additional MAC addresses. If that doesn’t work then try using the routed network as per the guide you originally linked to.