page size correctly set to A4 but print size still fixed to letter

Managed to get default page size to be A4, but every time I print it resets to letter.
Others said that you have to set the language to match the locale, but there is not an option for Australian english.

Have you checked your printer configuration in the OS? The driver may be configured by default to Letter. Driver and page style formats can live independently from each other. It is better to synchronise them.

Apologies, the language advice turned out to be a red herring.
Before asking the above I did experiment quite a bit, and seek some advice from online searches.

Below is not the ideal solution, I would have liked a solution that when you change print size in print settings you can set it as default print size so it works for all subsequent documents, unless overwritten. Or a way to make print size default to the page size for that document.

Workaround: For new documents, create a blank document called “default” with page size set and print settings set; then under File > templates, save as template (ticking the set to default option) under ALL possible categories.