In fact, you can print from iPhone without AirPrint. A special casing is a printer whose manufacturers have created certain applications that manage to print directly, without going through AirPrint. But more generally, it also includes printers that do not have a wireless section, you can do so by putting it between the computers that act as a bridge between iOS and a printer connected via USB.
So that's why you can print from iPhone without AirPrint. Here are the three most common options for this type of printing.
1.Printopia
Printopia is the most commonly used solution for printing without AirPrint. It is installed as a System Preferences panel and does not require the use of certain apps on iPhone. The iOS printing function is sufficient.
In addition to enabling us to print from iPhone without AirPrint, this software allows several functions related to the concept of virtual printing. For example, it stores prints directly to a Mac or PC, as a PDF or image file instead of actually printing it.
2. Printer Pro
Printer Pro comes from Readdle, a well-known software on iOS. It provides printing from the iPhone without AirPrint but from within certain applications, which allows multiple type operations. If the app detects a compatible printer over Wi-Fi, first, the app can print instantly, without going through the computer.
For the USB printer that you are using, not through the Printer Pro Desktop, a small application is available for MacOS and Windows and which acts as an interpreter as in the case of Printopia. But this is not a System Preferences panel but a stand-alone software.
3. handyPrint
handyPrint by Netputing is a lesser-known solution compared to the other two but with loyal users. Mac only, because it is not in the Windows version. Recently it has been a stand-alone application (to Printer Pro Desktop) while before it was a System Preferences panel (for Printopia).
Printing from an iPhone without AirPrint, therefore, involves only sharing printers connected via USB. All the "classic" printing functions are supported, as well as some virtual printing to store documents on a Mac.