All my programs will print 2 sided. Libre Office is the only one that will not print 2 sided if I create a 2 or more sheet Writer document. This is NOT a driver problem with my printer. It works for everything else, including Open Office and if I run Microsoft Office in Wind. I don’t like those I prefer to use Libre Office, but it is the only one I have problems with printing. I often need to manually start the printer because for some unknown reason it gets held. I only have this problem since updating LibreOffice. I cannot find help on line only excuses that it is my printer driver which it is not or the others would not work. I set the printer options to 2 sided, but since LO does not have an option to send a 2 sided CMD to the printer it will never print 2 sided. Printer is an HP OfficeJetPro 7740, OS is MX Linux.
Have you installed the CUPS package to manage printing? If so, File>Printer Settings and press the Properties button. The Paper tab has a Duplex drop-down menu with printer-specific choices.
I drive my old LaserWriter with the HP LaserJet 9000 MFP parameters. This model has no duplex engine and the choice is only Off (1-Sided) but other models have more options.
Have you clicked on the ▲more under Range and Copies in the print dialog from Writer (Ctrl+P) to see the paper sides options? Single/Duplex (portrait)/Duplex (landscape) are set there. Cheers, Al
Afterthought. On LO 7.0.1.2 Mint Linux Writer is not picking up the default setting from the Printer however it remembers the settings from last print even for new job after LO restart. Ideally, for a new job it should always use the default printer settings, not the last settings. Grump.
can confirm that downgrading to Libreoffice 6.3.1 (it has been said here problem started to occur with 6.3.5+) solved the issue; my Ecotank printer from Epson would also not duplex print in Libreoffice 7, or newer OpenOffice. However, in older version, it would.
https://downloadarchive.documentfoundation.org/libreoffice/old/
https://downloadarchive.documentfoundation.org/libreoffice/old/6.3.1.1/deb/x86_64/