Hey Filip,
I am also not able to discover the device via USB-C using the command adb devices
There are no link lights blinking on the port of my ethernet switch when plugged in either.
To ensure I provide as much detail as possible on this -> I have my Oak4D connected to my PoE+ Injector for the power, with another ethernet cable running from the PoE injector to my router. From this I'm still unable to discover the device on my network. This returns "List of devices attached" but this list is empty.
One thing I've not tried is ensuring that the device is plugged into my ethernet switch, power and connected via USB to my device