Did you just update the Marantz?
Can you verify that other parts are working, not just the network is failed?
Marantz / Denon AV receivers do not have USB DAC input. They have USB type-A port but it's for USB storage:
To access Marantz / Denon AV receivers internal DAC, you'd need to use coaxial or toslink or HDMI audio (not i2s).
If you use a PC for Roon Core, you can try connecting the PC HDMI output to the Marantz HDMI input. It may need some manual Roon configuration before you'll get sound though.
Can you verify that other parts are working, not just the network is failed?
Marantz / Denon AV receivers do not have USB DAC input. They have USB type-A port but it's for USB storage:

To access Marantz / Denon AV receivers internal DAC, you'd need to use coaxial or toslink or HDMI audio (not i2s).
If you use a PC for Roon Core, you can try connecting the PC HDMI output to the Marantz HDMI input. It may need some manual Roon configuration before you'll get sound though.