I can confirm that adding RequiredForOnline=no to the unconfigured interface's .network file resolves the timeout issue.
I did want to ask about the broader user experience: "apt-helper wait-online" calls "systemd-networkd-wait-online" without any interface arguments, which means it waits for all interfaces systemd-networkd manages. For users with unconfigured interfaces (secondary ethernet, unused wifi cards on servers, etc.), this causes a 30-second delay on every apt-daily run. While the RequiredForOnline=no solution works, it requires users to know about this systemd-networkd option and manually create .network files. Would it be worth considering one of the following? * A configuration option in apt to specify which interfaces to wait for * Documenting this behavior more prominently in apt's documentation? The current behavior was surprising to me, since I had expected apt to work without manual systemd-networkd configuration.
