printer connection

Hi,

Do you mean MP780?

If so, Canon does not appear to support anything later than Mac OS X 10.6.

https://www.usa.canon.com/internet/portal/us/home/support/details/printers/support-inkjet-printer/mp-series/pixma-mp780/pixma-mp780?tab=drivers_downloads

If necessary, you could perhaps have a look at the Gutenprint drivers. There are two experimental MP780 drivers in the list (http://gimp-print.sourceforge.net/p_Supported_Printers.php). Please note that there may be installation problems with macOS Catalina, according to the home page.

Safely open apps on your Mac - Apple Support

Reset the Mac printing system to solve a problem - Apple Support

Add a printer on Mac - Apple Support

Contact Canon for support or buy an AirPrint-enabled printer.