Lost ability to print both sides

[EdwinVance]

Now using MS Office for Mac, via Office Home & Student 2019 ( previous to this I had been using MS Office 365). Wondered if this is cause of problem?

Always used the both sides facility printing from Word, "paper handling". Now the Print "Box" doesn't show this facility. Instead it will say "using one sheet of paper" which I took to mean printing on both sides, but, no, it prints two sheets of paper, not one!

It's driving me nuts

[EdwinVance · Accepted solution]

Suddenly, without doing anything different, the "old "and familiar Print box appeared, with its facility for printing both sides. Then the printing stopped and I got the Message:

"Paper size mismatch

The paper size detected by the printer sensor does not match the paper size selected by in software.

If the paper loaded in the printer is the correct size, change the selected paper size in your software and re-send the print job.

If the paper loaded in the printer is not the correct size, change the paper and re-send the print job.

To cancel the print job, click Cancel Print"

AND the paper jammed. 

I have cleared the jam 

It seems, somehow the default paper size had changed from A4. Eventually, with much trial and error, I have printed a two sided document.

Sorry to have troubled the Community. I have solved my own problem!!