We have an ancient Canon MG8120 Printer/Scanner and it actually still works even with Macs on Catalina even though the software tools are advertised as good through MacOS 10.6. However some of the utilities stopped working as the MacOS progressed. The MF Toolbox should work through 10.14, however, so you should not be seeing this issue.
You might try the following, one at a time, to see if any resolve the issue:
- Look for the preference files in your user Library folder, Preferences, and then look for any support files or folders with the text "canon" in them. I have an entire folder called Canon there and it has various scanner preference files. You can also use a program like Find Any File to search everywhere on your Mac for "Canon" and "Toolbox" to find all such support files, both in the Preferences as well as Application Support folder (which is also in the Library). You may get lots of false "hits," but going through them one by one may pay off. You can try moving these files to a safe place, rebooting, and then seeing if the program functions properly. The files can be restored if they are found to not be related to the problem.
- You can try reinstalling the Toolbox program. It would best to first uninstall it, but that may not be straightforward.
- More drastic is to completely remove/delete the printer/scanner from your list in System Preferences and then reinstall everything and add the device back to your printer/scanner list.
On my Canon MG8120 I have reinstalled software, drivers, utilities a few times. The Canon utilities are nice to have but sometimes they are "quirky."
You can also try using Image Capture to scan from your device. This will almost certainly work. You can start up Image Capture and tell it to look for your scanner or often you can start it up from the Printer or Scanner System Preferences pane. You should be able to use the Toolbox but using Image Capture can be consider a band aid until you can figure out what happened.
