Duplex printing on other than A4 not working

[Gordonbp]

LO Version: 6.1.5.2 Build ID: 1:6.1.5-3+deb10u7 on MX Linux
Printer: ENVY 5640 series wireless connected

I have a multi page document that I want to print as a brochure but smaller than A5 on A4 paper - ie so I trim the excess paper to create the size I want.
It seems that the Duplex function, although turned on and set to bind on the short edge, doesn’t function unless I use A4 as the paper size, which produces an A5 brochure which I don’t want!
Is there any solution to this?

[ajlittoz]

When I need to produce non-standard sized documents, I cheat: I use standard size and I adjust the margins to match my target format. Caution! With duplex printing, the margins are different on odd and even pages. Take this into account when defining your page style(s).

[LeroyG]

You can “trim the excess paper to create the size” you want, then print duplex.