How to install a driver for the HP Deskjet 5550 on macOS 10.14?
You can use the Gutenprint drivers:
https://sourceforge.net/projects/gimp-print/files/

Click the "Download Latest Version" button.

Once you have downloaded the disk image and installed the drivers, make sure the printer is connected and powered up, then re-add your printer in System Preferences > Printer &amp; Scanners.  It should automatically select the Gutenprint driver.  Otherwise, manually select it.

Click "Add" and you are ready to print.