Even if a UR-C or an AXR4 is connected to the system, there are cases that the Input Settings Window of the audio interface (see below) cannot be found in the Inspector in the Project Window of Cubase/Nuendo.
The Input Settings Window of a UR-C or an AXR4 appears when the input and output device ports of the audio interface are assigned to the input and output busses of an audio track in the Project Window of Cubase/Nuendo and the 'Hardware' category visibility is enabled in the Inspector setup (right-click in an empty part of the Inspector).
Assign the input and output device ports accordingly. These have to be set in the 'Studio' ▸ 'Audio Connections'.
Then set the input and output for the desired audio track.
In case Cubase Pro and Nuendo are used, the input or output device ports which are already used for the Control Room cannot be used for an audio track. Please use the remaining input and output device ports, or disable the Control Room function if no other input and output device ports are available.