Hi @gz2,
I'd like to help!
When you set up a duplex printing job, the settings might carry over to the next print job. Additionally, some HP printers come with duplex printing set as the default. To change back to one-sided printing, turn off the duplex setting in the print window.
To preserve duplex or one-sided settings for future print jobs, complete the print job with the desired settings, click the Presets menu, select Save Current Settings as Preset, and then give the preset a name such as One-Sided Documents.

You may refer to -How to Print on Both Sides of the Paper (Duplex) (Mac)
Hope this helps! Keep me posted.
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