Open CUPS Settings in Your Browser
To enable CUPS web interface please refer to this article > https://support.drlogic.com/hc/en-us/articles/360002273478-Enabling-CUPS-Printer-Web-Interface-for-Mac
Open up your web browser (Chrome is best) and head to http://localhost:631. Clicking that link should work, but copy and paste the URL if it doesn’t. If everything is working, you’ll find yourself at the CUPS settings home page. You’re accessing this through a browser, but the page isn’t online: everything you’re seeing is on your computer.
You will be asked for a username and password; enter the credentials you use to log into your Mac.
Step Three: Find and Change the Two-Side Printing Option
In the CUPS settings, head to the “Printers” section, where you’ll see a list of printers. Click the printer for which you want to change settings and you’ll be taken to the printer’s configuration page. Click the “Administration” dropdown menu.
In the list that opens, click “Set Default Options.”
You’re taken to a page that shows a series of dropdown menus controlling various default options. The one you’re looking for is named “2-Sided Printing.”
Click this dropdown, and then select “Off (1-Sided)” from the list of options. Click the “Set Default Options” button to save your changes.
And you’re done! You can now close your browser. To test the changes, just print any document. You’ll see that two-sided printing is no longer enabled by default.