iOS/iPadOS doesn’t natively support direct connection to a USB Printer. Instead, these devices use a network connection to supported printers typically over WiFi - or if explicitly supported by the printer, a wired ethernet connection. Some printers also support WiFi Direct printing - where the printer creates its own stand-alone WiFi network for printing.
See:
Apple AirPrint is a driverless connection protocol. A high proportion of modern printers intended for Home, SoHo and Business environments now support AirPrint. Check your printer model against this list:
About AirPrint - Apple Support
If your printer is not compatible with AirPrint, there are alternatives…
Some printer manufacturers have a suitable companion App that provides Print capabilities for mobile devices, often using a web-based print service. Others can print directly if the App supports other network printing protocols. By example, many HP Printers use the HP Smart App - available in the App Store:
https://apps.apple.com/gb/app/hp-smart/id469284907
You might also consider connecting a non-AirPrint printer to a PC or Mac computer - and install a “helper application” that allows the computer to emulate AirPrint capabilities; one such option is Readdle Printer Pro, for which suitable software for PC is available. A link to the PC software is included from this page:
https://readdle.com/printerpro
A further alternative is to consider installing a dedicated Print Server Appliance on your network - and connect your printer to this. One example is the Lantronix xPrintServer.
The remaining solution is to simply replace your printer with one that is AirPrint capable.
