From the screenshot below, it is only the Primary Work Process(PWP) is being assigned a port number. Other WPs are not assigned any port number.
Release : 12.3
Component : Automation Engine
It is normal behavior in v12.3 that only the Primary Work Process has a defined port number in UCsrv.ini file. In fact, other WPs will connect to the PWP and to the CPs. Therefore, you do not have to assign ports for WPs in INI file of the AE. This behavior is explained in section "Work Processes (WP) and Primary Work Process (PWP)".