Getting double-sided printing working on a HP printer in Windows 10

For whatever reason, every few years, it seems like I struggle with double-sided printing.  This is what finally worked for me: https://h30434.www3.hp.com/t5/LaserJet-Printing/Duplex-printing-disabled-in-Windows-10/td-p/5521457

The trick was to open "Devices and Printers" in the control panel, left double-click on the printer, click on "Customize your printer, and click on the "Device Settings" tab.  Choose "Installed" for "Installable Options -> Duplex Unit".

I'm not sure why that dialog is so hard to find.