10-18-2020 08:54 AM - edited 10-18-2020 08:57 AM
I'm having this problem too with my Mac running Sierra. When I first got the mf743cdw, I was able to install the scanner driver and used it once, but since then my computer hasn't been able to find it. I can't add my printer at all through the MF Toolbox using either Bonjour or the IP address (it says the "specified scanner is not supported"), and while I can add it to the MF Scan Utility (and believe me, I've been saying "MF!" a lot during this process), it appears in Bonjour and I can add the IP address, but it says it cannoy commuicate with the scanner. Tried reinstalling and uninstalling, but nothing works. I can connect through Remote UI no problem and it shows the scanner is ready. Canon really needs to fix this problem with the drivers, it is extremely frustrating. Couple that with the fact that we're using the same unit with 3 other computers (Mac and PC), so any change in IP address or network settings makes those computers unable to find the printer.
The good news is that I did find a workaround. If I go into the Settings/Printers & Scanners, and then select the "Scan" tab there's a button to "Open Scanner" which opens Apple's built-in scanner interface... it's not great to work with, but I can indeed scan without having to reinstall anything. Also, I need to wake up the printer sometimes before it will work, but damnit, I can scan!