This option is available only to protocols such as X-Window whose client-server meanings are reversed. If you are uncertain, leave this option cleared.
Review the below link.
The weird thing is, in my environment I only has the option of sepcifying 'main server IP address' and 'NLB NAT masking IP address', but there is not checkbox of client port(s)
I am running DCRUM2017 SP3.
For which analyzer you are creating a software service?
As mentioned in the document that this option is only available for the X-Window protocol.
The X Window System core protocol is the base protocol of the X Window System, which is a networkedwindowing system for bitmap displays used to build graphical user interfaces on Unix, Unix-like, and other operating systems. The X Window System is based on a client–server model: a single server controls the input/outputhardware, such as the screen, the keyboard, and the mouse; all application programs act as clients, interacting with the user and with the other clients via the server. This interaction is regulated by the X Window System core protocol.
Just check with the Generic, Generic (with transactions), TCP etc... whether you can see this option or not.
The other example is a ICA (Citrix) analyzer where you can find this option.