No ttyACM0 with Pro Micro on Ubuntu 18.04
A Pro Micro will only give a /dev/ttyACMx device node if the firmware installed on it creates a CDC/ACM interface.  That device obviously is running custom firmware which only provides the interfaces that the manufacturer wants to provide - in this case keyboard and mouse interfaces.

To use it as an Arduino you will first have to install the Arduino bootloader. That will then remove the existing manufacturer firmware, and you will have to write your own to make it act as a keyboard again.