That printer is no longer supported on Mac OS by Canon. Suggest you visit: https://www.usa.canon.com/internet/portal/us/home/support/details/printers/support-inkjet-printer/mg-series/pixma-mg6120/pixma-mg6120?tab=drivers_downloads
to find comparable printers that are.
You might be able to add the printer using the Option key to Apple menu -> System Preferences -> Printers -> Add printer printer using the plus sign button on the window itself under the printer. Especially if you connect the printer via USB, or make sure it already is working on the same secure WiFi network as your phone, and you can print from the phone, and your computer is sharing that same network.
If neither works, it may be time to also consider installing the last OS that was compatible with the printer on your Mac, if your Mac is compatible with older OSes.
Backup your data before installing anything or partitioning.
Be sure it is HFS Extended if the system is older than High Sierra. Macs can only run the system that was available at the time if their release and newer systems up to the hardware limitations. To install the oldest OS, enable internet restore at startup with command-option-shift-R. You can't install an older system directly on a system that is newer.
iOS is the operating system found on the iPad and iPhone. Mac OS is the operating system found on any machine named Macintosh.