Use remote serial port as a local one

Note that "virtual serial port" is Windows terminology; Linux doesn't have "virtual serial ports".

What Linux has is a file that supports additional ioctls; if you don't need those, you can try redirection with tools like socat.

If you do need those, I don't know a solution. However, what you can do is forward USB devices transparently over the network using e.g. usbip. Most Linux distros will have usbip included as packages.

So you treat the USB serial port on the remote device as a local USB device, and then access /dev/ttyUSBX on the local device.

This will also forward the USB packets representing DTR, RTS etc. operations in both directions.