Comment 16 for bug 2063331

I'm guessing this is what's happening in your scenario:

ubuntu-desktop will install ubuntu-settings as one of its dependencies. ubuntu-settings will install "/lib/netplan/00-network-manager-all.yaml". This configuration file will delegate the network configuration to Network Manager.

In this case, networkd will not manage any of your NICs and networkd-wait-online will block waiting for any of the interfaces it manages to become online. As it doesn't manage any interfaces, it will block until it times out. I see it as a problem with the networkd-wait-online logic.

For your scenario, I'd suggest you to disable the wait-online service:

systemctl disable systemd-networkd-wait-online

Or, you can just not use Network Manager by adding "renderer: networkd" to your main config file in /etc/netplan. But if you need ubuntu-desktop you probably want to use Network Manager.