The port number can be anything you want and can be set however you want. Roon picks a default of 55000, unless that port is in use already, then it picks another default.
Okay, makes sense. I was wondering why it was choosing that port. I would suggest anyone having trouble to look at this in the software when it does the test. I had opened port forwarding on 55000 and it was not working and noticed this in the output. No idea what is using it on my network. Netgear Nighthawk 7000,