Insists on printing on both sides regardless of setting..
I’m going to assume you’re on Mac since this is a common Mac problem.
Interface may differ a bit depending on Printer and OS version.

How-To: Turn Off Duplex Printing by Default on Your Mac
I’ve been a Mac since 2006. That was the first year that Apple produced an Intel-based Mac, and I remain a Mac to this day. I will likely be a Mac for many years to come. One of the biggest issues I have with my Canon Multi-Function Laser…
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This is, I believe, a Dorico issue, not a Mac issue (although it may only affect Dorico on Macs?). I have duplex printing turned off wherever it is an option, using an HP printer, and Dorico insists on always printing double-sided anyway, when no other app does. Exporting to PDF and then printing the PDF (using the default print options) seems to be the only way to avoid it.
This. It has always worked in Dorico, independent of the setting in the Mac OS Print Dialog. For some reason Today it won’t print single-sided. 1 page at a time, OK, but it’s another of Dorico’s idiosyncrasies.
There IS a solution and when I can find the youtube video for it I’ll post it. It involves going deep into printer settings but is doable.
You’ll find lots of threads about this. It seems to affect some printer makes/models more than others – particularly Brother.
The issue is (… handwaves…) something to do with how they interpret the message that Dorico sends for “no duplexing”. Some interpret it as “go back to the default state”, which may still be duplexed.
In short: if you configure your printer to single-sided by default, you should be ok.
Isn’t it the video Craig_F posted above?
