If it found it, there should be no need to add it again. simply unlock the Settings window, right click, set as default and then right click again, select properties and locate print test page. It should work if Ubuntu found it. from there if it does not works.
Open a terminal run sudo apt update && sudo apt list --upgradable
then sudo apt upgrade -y
Allow the updates, log out of session or reboot and try the test page again.
one thing about “network” printers that most annoying is they change IP addresses.
Suggest going through the actual physical printer settings. write down the current IP and MAC address and add it to your router as a static IP for that MAC address. Unlock settings and then point the printer to that IP address.
I’m finally able to try out your suggestion. 2 items; 1) I have seen or needed to “unlock” the Printers dialogue box, am I missing something? 2) In the Printer window below, where do I insert the IP Address and Mac Address for my printer?
Glad you have it working,
Fortunately I have never had to use any manufacturers programs: Epson, HP, Lexmark or Cannons that I have had in the last 10 years.
Ubuntu was by far the easiest to get any of my printers running on but can say, Debian has been pretty much a breeze there as well.