Unfortunately, the Man Page: https://netplan.io/reference is not precise in the description for the optional (bool) property.
If one interface has this setting:
ethernets: eth0: optional: true
and the Interface gets online some time after the boot sequence, does networkd initialize it as soon as it detects the Interface?
I ask how it is designed/meant to be and not how a specific OS Version implements it :-)
Thanks a lot for any help!