Looks like my driver is not seeing duplex on LJ Pro M426fdn and claims it is not present.

[Jno_Eagle]

April 2021 printer began printing one-side only.  For a while, 5 or 6 weeks, could correct in Windows 10 64Bit.  Now duplex is "not present" and Win 10 resetting no longer available.  Some places at HP site still admit duplex is present but the config report shows"Duplex: Off" under Paper Settings. Looking around on HP site seems probable the problem is the driver.  This is an ethernet or usb connected printer, but have wifi if there is such a thing as an adapter/connection.  5 or 6 year old printer works fine except for this problem. 

[ShlomiL]

Hi,
Make sure the Automatic Duplexing option is enabled:

Enter Control Panel > Devices and Printers.
Right click the printer icon, then click Printer Properties.
Click the Device Settings tab.
Set the Automatic Two-Sided Duplex Accessory as installed and click OK to save the change.

Now Automatic Duplexing should become available.

Regards,
Shlomi

[Jno_Eagle]

I was with you up to "Device Settings" which does not appear on my setup.  I must have a different version of Win 10 64bit.  I am trying to take a screen shot with the 3 pertinent screens reduced and showing on one picture, but and have the image set on the screen,  If I cannot get a screen shot, will take an iPhone pic and send it.  I will mark it for the author of the current response.

If someone can give me an address at HP Forums it would be much appreciated.  My monitor is a curved Samsung so the pic will look curved top and bottom, but should be legible on a monitor.  I can read it on my iPhone with a little finger spread.  Thanks for the help. 

[ShlomiL]

Please make sure that you select Printer Properties after right-clicking the printer icon and not Properties, just making sure as this is quite a common error, please attach the screenshot if above doesn’t help.