I have a Canon Imageclass MF4570dw printer on Elementary OS Juno and I can't print double sided, it is disabled in the settings panel and says "not available" in the printing dialog. See the attached screenshots. I have the canon-supplied driver for it. It's recognized as Canon-MF4700-Series-UFRII-LT. I tried this solution from user drs305 to get access to the cups "modify printer" menu, but as you can see in the attached screenshot, the only thing I can get to is the description of the printer.
