The key to the solution of your question is to clearly understand the document model implied by Writer.
The application by itself has no defaults, apart from a very small number of them set in Tools
>Options
in various “sections” of the dialog.
When you open a document, its initial state is copied from the designated template. If you didn’t explicitly choose a template, the “default template”, whether “factory-made” or user-designated as such, is used.
The template brings in a collection of styles: paragraph, character, frame, page and “list”. The “geometry” of the document is defined in the page styles. Page styles have provision to define columns and their relationship.
To create your default, start with a blank document, modify its styles and save it as a template. Make it the default template and your done.
The initial page style is Default Page Style, but if you routinely use others, customise them as well.
- In the toolbar of the side style pane (
F11
if not already visible), click on the fourth icon from left to list the page styles
- Right-click on Default Page Style and
Modify
- In the
Columns
tab, set the number of columns, their width if relevant and the spacing between columns
- Tune the other parameters if needed: margins, header or footer occurrence, …
- Press
OK
Do the same for all other styles you’d like to configure to your taste (paragraph, character, …)
Next time you create a document, your preferences will be applied.
EDIT 2021-02-04
Columns are attributes of page styles. Note the plural form. In case your document has parts with different number of columns, create one page style per part kind (or part if these parts do not share common attributes such as header). You then Insert
>Break
>Manual Breaks
(not the traditional Ctrl
+Enter
) to be able to choose the page style to apply after the break.
This changes the number of columns on a page boundary. If you want to change it in the middle of a page, you must Insert
>Section
. Unfortunately, a section is always manually formatted because there is no “section style”. This means the properties of future sections can’t be saved in a template or anywhere. But remember that a section is supposed to introduce a temporary change. At end of the section, you revert to the page style “geometry”.
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