If an USB-connected printer is not detected by Cura, there is nothing you can do with the printer definition (*.def.json) that can fix this.
USB printing in Cura is not something that is actively supported by Ultimaker, because it has not been recommended or even possible with their printers to use USB printing. So the USB Printing that is provided by Cura is basically provided as-is. If it works, it works. If not: sorry, you are going to have to use other software to connect with the printer to print the gcode produced by Cura (eg PrintRun/pronterface, or OctoPrint).
Having said that, I am working - on and of - on a plugin that replaces the current USB Printing functionality with the functional part of pronterface. Progress is slow, mainly because I don't use direct USB printing myself either.
You can sponsor my work on this plugin (and others): https://github.com/sponsors/fieldofview
That is most likely due to Cura not connected to the printer.
Check under manager printers if it is listed or not
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