How to set up LAN Printer with IP address
I have been through a similar struggle, but a Brother HL-2250DN networked printer and Android Pie. Printer is not showing up when searching in Default Print Service.

I can see the Brother printer on the network using Fing, and can ping it by its IP address so it isn't a network problem.

The Brother supports Internet Protocol Printing (IPP) which is apparently supported by Android, but I'm not convinced Brother's implementation is good. It also supports other protocols supported by Android, but enabling them all doesn't make the printer show up.

I discovered if I shared the printer from my Mac, it did then show up in Default Print Service, and I can print from my Android. Unfortunately, sharing from Windows doesn't seem to work in this way.

It would be nice not to need another client powered on in order to print, but that probably requires a printer natively supporting Google Cloud Print or properly implementing an Android supported promoting protocol.