I’m trying to create a document with 12 x A4 portrait with normal text and 2 x A4 landscape with a table on it. How do I achieve this please? It changes the whole document when I try to change just 2 pages! Please tell me this is possible!
TIA
Orientation is a property of page style. Consequently, to switch from portrait to landscape, you must insert a page break (manually or through an ad hoc style) and select the desired page style after the break. Built-in Landscape is intended for that while Default Style is in portrait orientation.
You are encouraged to read the Writer Guide to discover what can be done with styles.
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I tried that 
it still did the whole document even with a page break (CTRL-Enter)
That’s not good enough, you need to do Insert - Manual break, then select landscape or portrait page style from the list.
Thank you so much, that worked! I’ve been using Open/Libre Office for years, but never had to do this before for my Daughter In Law’s Literary Review for her final year of Nursing - you’ve saved both of our sanity. 