Its a macOS 10.14 issue. Either upgrade to 10.15 to fix library validation or invoke the workaround, which is to use a 3rd party app Like Adobe Reader DC to get the Xerox Features entry in the print driver, save the duplex setting as a preset and use the Preset in all the Apple sandbox apps that show Printer Features instead of the proper Xerox Features
Hi after many years i m moving to apple and macos mojave
My printer at windows pc enviroment printing duplex perfect for almost two year.
At my macbook pto install the proper driver but the duplex unit control is not working