The issue is that apparently there isn't any available driver. CUPS recognizes that there is a printer connected to the serial port, and it lets me install it. I used CUPS to try to manage it, up to now.
I'm trying now to make that printer work. In such old computer, which is the only one I have with a serial port, I installed a Linux operating system, which works quite fine. Both for fun and for artistic projects I'm trying to connect an old dot matrix printer, the Panasonic KX-P1170, to a certain old computer.