HP M479fdw duplex settings gone missing

[BoMc]

I've had this HP M479fdw for 2 years. It has worked pretty much flawlessly. I use HP toner carts exclusively. Firmware is CLRWTRXXXN002.2539E.00.

In the last couple of weeks, the duplex settings disappeared. How do I get them back? 

Thanks.

[MacFixerX]

I’m facing the same issue: the duplex option has disappeared. I believe it happened after upgrading from the previous macOS version to 26.2. I’ve tried reinstalling multiple times using both the HP app and the basic Bonjour protocol, but neither method restores the duplex feature.

[MacFixerX]

After some trial and error, what worked was enabling the duplex setting by default in the printer’s web interface. Once I did that, macOS recognized the duplex option.