My Mac Mini uses my ‘old’ Canon Pixma MX850 as a network scanner. I can either say to the Mac that it should scan using the Pixma, or I can tell the scanner from the machine operation panel to scan images and then place them on the Mac Mini (or indeed one of the other networked machines on the LAN). But I inadvertently used the top bar scanner selection utility (Canon IJ Network Scanner Selector)
and picked on the ‘Do Not Use’ option.
Bad idea because the listed scanner MAC address immediately disappeared. No problem I thought, I’ll just rescan. There isn’t a rescan option. In fact there was no way I could find to get the scanner listed again. In the end, the only way to recover the situation was to reinstall the Canon MX850 Scanner Driver software from the Canon support site.
Now you can one again see the Mac as a target from the Pixma operations panel: