I think it is possible, but I am not sure. Because, NanoPC-T6 has a USB-C port that supports DisplayPort (DP), the possibility of connecting to your Viewsonic TD1655 monitor with a single cable is possible. However, to be sure, check the USB-C port details on both NanoPC-T6 and the monitor. If both support DisplayPort and PD, you can use single-cable mode.
You should check the technical information of both devices before purchasing to avoid risks.